Prognostic effect of low-level HER2 expression in patients with clinically negative HER2 status

Interobserver agreement in scoring HER2-negative and HER2-low immunohistochemistry in breast cancer: Reasons for discordance and impact of a single training session

OBJECTIVE

In the DESTINY-Breast04 trial, human epidermal growth factor receptor 2 (HER2) low (HER2-L) is defined as an HER2 immunohistochemistry (IHC) score of 1+ or 2+ with negative fluorescence in situ hybridization. Limited data report poor agreement in scoring HER2-0 vs 1+. We aim to investigate the HER2 IHC concordance rate, with focus on HER2-0 vs HER2-L groups. We evaluate the impact of a single training session on concordance.

METHODS

Nine breast pathologists from the same institution reviewed 60 HER2 IHC stains on breast biopsy specimens in 2 rounds of 30 cases each. An educational slide review session was provided between the 2 rounds. Interobserver Cohen κ values were computed and compared.

RESULTS

Overall complete agreement for HER2 IHC was noted in 37 (62%) of 60 cases, with similar agreement in the first round (19/30 [63%]) and second round (18/30 [60%]). For all 60 cases, κ values ranged from .517 to .895, with 92% of κ values in substantial agreement or better range. For combined HER2-0 and HER2-L cases, κ values ranged from .298 to .826, with only 45% of κ values in substantial agreement or better range. In HER2-L only cases, 50% of the scorer pairs of κ values were 0 or less (no agreement), and only 14% of pairs showed substantial or better agreement. The educational session did not improve the κ values. Faint and heterogeneous HER2 expression, cytoplasmic blush, dislodged cells, and in situ component led to poor concordance in HER2-0 vs HER2-L.

CONCLUSIONS

Poor concordance on HER2-0 vs HER2-L and lack of improvement after a training session likely suggest ineffective HER2 IHC expression range in HER2 low spectrum.

From text to insight: A natural language processing-based analysis of burst and research trends in HER2-low breast cancer patients

With the intensification of population aging, the proportion of elderly breast cancer patients is continuously increasing, among which those with low HER2 expression account for approximately 45 %-55 % of all cases within traditional HER2-negative breast cancer. Concurrently, the significant therapeutic effect of T-DXd on patients with HER2-low tumors has brought this group into the public spotlight. Since the clinical approval of T-DXd in 2019, there has been a significant vertical surge in the volume of publications within this domain. We analyzed 512 articles on HER2-low breast cancer from the Web of Science Core Collection using bibliometrics, topic modeling, and knowledge graph techniques to summarize the current state and trends of research in this domain. Research efforts are particularly concentrated in the United States and China. Our analysis revealed six main research directions: HER2 detection, omics and clinical biomarkers, basic and translational research, neoadjuvant therapy and prognosis, progress of ADC drugs and clinical trials. To enhance the therapeutic efficacy and safety of antibodydrug conjugates (ADCs), researchers are actively exploring potential drug candidates other than T-DXd, with numerous ADC drugs emerging in clinical practice and trials. By incorporating emerging treatment strategies such as immunotherapy and employing circulating tumor cell (CTC) detection techniques, progress has been made toward improving the prognosis of patients with low HER2 expression. We believe that these research efforts hold promise as compelling evidence that HER2-low breast cancer may constitute a distinct and independent subtype.

Activity and Efficacy of Neoadjuvant Chemotherapy in Luminal-HER2 Negative Early Breast Cancer According to HER2 Score (Low vs. Score 0): A Retrospective Study

BACKGROUND

The predictive and prognostic role of HER2 status in patients with luminal-HER2 negative early breast cancer (BC) undergoing neoadjuvant chemotherapy is unclear. A retrospective analysis evaluating the correlation between HER2 status (low vs. score 0) and pCR/IDFS was conducted.

METHODS

Patients with BC undergoing neoadjuvant chemotherapy and surgery were included. HER2 low BC was defined as IHC 1+ or 2+ with negative FISH. Logistic regression model and Cox proportional hazard model were adopted to investigate the independent role of HER2 status and outcomes of interest (pCR, CPS-EG and IDFS).

RESULTS

About 566 patients were included: 60% were HER2 low and 40% were HER2 0. pCR was achieved in 13.2% of HER2 low versus 17.7% of HER2 0 (P = .15). There was no correlation between baseline HER2 status and CPS-EG score (P = .18). A trend toward improved IDFS for HER2 low BC was observed (P = .07). The relapse rate of the HER2 0 cohort peaked at 12 months after surgery, similar to the HER2 low cohort, which showed an additional peak at 36 months after surgery.

CONCLUSIONS

Among Luminal-HER2 negative early BCs, our results do not support a clear predictive and prognostic effect of HER2 status, although a trend of worse pCR and better survival for HER2 low BCs cannot be ruled out.

First-line carboplatin-based chemotherapy may be beneficial for HER2-low advanced breast cancer: A retrospective analysis

For patients with human epidermal growth factor receptor 2 (HER2)-low advanced breast cancer who had failed to meet with anthracycline or taxane, the application of HER2-targeted antibody-drug conjugates as second-line therapy could improve patients' outcomes, but it is unclear whether carboplatin-based first-line therapy will benefit these patients. This retrospective study was designed to explore whether carboplatin based first-line treatment could improve outcomes in HER2-low advanced breast cancer, and to analyze potential factors affecting efficacy and prognosis. 103 patients with HER2-negative metastatic breast cancer were treated with carboplatin based first-line therapy. The differences in progression-free survival (PFS), objective response rate (ORR), and adverse events were analyzed in different HER2 expression subgroups. The risk ratio (HR) and 95% confidence interval (CI) for PFS were estimated using Cox proportional risk models. The ORR for the whole group was 42.72% and the median PFS (mPFS) was 7.93 months (m). The ORR of HER2-low patients was significantly higher than HER2-zero patients (56.4% vs 27.1%, P = .003), and HER2-zero was an independent risk factor of ORR (OR 3.478, 95%CI 1.516-7.977, P = .003), especially in the HR-negative subgroup. The mPFS was significantly longer in patients with low neutrophil-to-lymphocyte ratio (NLR) scores than those with high NLR scores (P < .001). Multivariate analysis showed that young breast cancer (age < 40) (P = .006) and high NLR values (P = .001) were prognostic risk factors affecting mPFS. The main grade 3 to 4 adverse reactions were neutropenia (15.53%), anemia (15.53%), and leukopenia (11.65%). The first-line carboplatin-based chemotherapy is quite active and tolerable in patients with HER2-low advanced breast cancer, that higher response rates can be achieved. In cases where CDK4/6 inhibitors are inappropriate for use due to resistance to endocrine therapy or the urgent need for short-term clinical response, chemotherapy remains important. When it is necessary to consider the accessibility of antibody-drug conjugates and the economics of patients, carboplatin-based chemotherapy may be provided to HER2-low patients as a more convenient, cost-effective and efficient option on the front line. Forecasting the efficacy and prognosis via inflammatory index such as NLR before the commencement of the treatment could enhance the precision and efficiency of carboplatin-based regimens.

Clinicopathological characteristics, evolution, and treatment outcomes of hormone receptor-negative/HER2-low metastatic breast cancer: a pooled analysis of individual patient data from three prospective clinical trials

Objective

With the approval of trastuzumab deruxtecan for the treatment of unresectable/metastatic HER2-low breast cancer, human epidermal growth factor receptor 2 (HER2)-low has emerged as a clinically actionable biomarker. There is an urgent need for a deeper understanding of HER2-low breast cancer patients. Therefore, this study was conducted to explore the clinicopathological characteristics, the evolution of HER2-low status, and its impact on the prognosis of hormone receptor (HoR)-negative/HER2-low metastatic breast cancer (MBC) patients.

Methods

This pooled analysis included 350 metastatic triple-negative breast cancer (mTNBC) patients who received first-line platinum-based chemotherapy at Fudan University Shanghai Cancer Center from November 2007 to July 2022. Patients were categorized into HER2-0 and HER2-low groups based on their HER2 status. Baseline clinicopathological characteristics, evolution of HER2 status between primary and metastatic lesions, and treatment efficacy were compared between the two groups.

Results

Among the 350 mTNBC patients, 34.9% (122/350) were HER2-low and 65.1% (228/350) were HER2-0. Significant differences were observed between HER2-low and HER2-0 patients in terms of age and menopausal status. HER2-low patients were older (54 vs. 49 years, p=0.002) and had a lower proportion of premenopausal patients (32.8% vs. 52.6%, p<0.001) compared to HER2-0 patients. No significant differences were observed in progression-free survival (PFS) and overall survival (OS) between HER2-low and HER2-0 patients receiving first-line platinum-based chemotherapy (mPFS: 7.43 vs. 8.30 months, p=0.389, HR=1.11, 95% CI 0.88-1.40; mOS: 25.37 vs. 26.63 months, p=0.907, HR=1.02, 95% CI 0.76-1.37). Additionally, 32.3% (41/127) of patients exhibited discordant HER2 status between primary and metastatic lesions, primarily evolving from HER2-0 to HER2-low. Notably, patients with discordant HER2 status had significantly longer PFS compared to those with concordant status (mPFS: 11.07 vs. 7.53 months, p=0.020). The Cox multivariate analysis showed that HER2 status consistency (p=0.026) was an independent predictor of PFS.

Conclusion

In mTNBC patients, those with HER2-low status had similar responses to platinum-based chemotherapy as HER2-0 patients. There was significant discordance in HER2 status between primary and metastatic lesions. Patients with discordant HER2 status had better responses to platinum-based chemotherapy. Therefore, for patients with HER2-0 primary lesions, re-evaluation of HER2 status in metastatic lesions through biopsy may offer new treatment opportunities.

The efficacy of trastuzumab-deruxtecan for the treatment of patients with advanced HER2-low breast cancer

INTRODUCTION

Until recently, the available human receptor epidermal growth factor 2 (HER2) targeted agents were ineffective for treating patients with HER2-low expressing breast cancer (defined as immunohistochemical expression of 1+ or 2+ without amplification). The development of novel and potent HER2-directed antibody-drug conjugates, affective at treating HER2-low expressing breast cancers, have changed the way we think about HER2-low expression and expanded the treatment options for many patients with advanced disease.

AREAS COVERED

In this review, we summarize the current management of HER2-low breast cancer and commonly encountered challenges such as treatment sequencing and toxicity management.

EXPERT OPINION

trastuzumab deruxtecan (T-DXd) is a treatment option for patients with advanced, HER2-low breast cancer, irrespective of the hormone receptor status. The current optimal place in treatment algorithms is after the first line of chemotherapy, both in HR-positive and triple-negative breast cancer; however, other agents are available in this setting and risks and benefits for each should be considered in shared decision making. Up to 10-15% of patients receiving T-DXd develop interstitial lung disease. Patient and clinician education are key to safely implement T-DXd in clinical practice.

Efficacy and prognosis of neoadjuvant chemotherapy in HER2 low-expressing breast cancer: a retrospective single-center study

Purpose

Human epidermal growth factor receptor 2 (HER2) is vital for breast cancer prognosis. The aim of this study was to analyze the clinicopathological data of HER2-negative breast cancer patients receiving neoadjuvant chemotherapy and the associated factors affecting the pathological complete response rate (pCR) and prognosis.

Methods

Clinical data of 173 patients with primary HER2-negative breast cancer, who initially received neoadjuvant chemotherapy followed by surgical treatment at the Breast Surgery Department of Bethune Hospital in Shanxi Province from January 2012 to December 2022, were collected.

Results

Compared to HER2-0 patients, HER2-low patients had higher T staging (p = 0.008), higher Ki67 proliferation index (p < 0.001), lower N staging (p = 0.001), and lower pCR rate (p < 0.001). Univariate analysis revealed that T stage, TNM stage, HR status, HER2 status, and Ki67 are risk factors that affect the pCR rate in HER-2 negative. Multivariate analysis identified HR status as an independent predictor of pCR rate. Kaplan-Meier survival curves showed that menstrual status, N staging, T staging, TNM staging, and pCR status affected the prognosis of HER2-low breast cancer patients (p < 0.05).

Conclusion

HER2-low breast cancer exhibits distinct biological behaviors, suggesting personalized treatment approaches.

Real-world treatment patterns and outcomes in patients with HR+/HER2- metastatic breast cancer treated with chemotherapy in the United States

BACKGROUND

Until recently, treatment options for patients with hormone receptor-positive/human epidermal growth factor 2-negative (HR+/HER2-) metastatic breast cancer (mBC) and resistance to endocrine therapy were limited to chemotherapy. This real-world study describes treatment patterns and outcomes in patients treated with chemotherapy in the United States before approval of antibody-drug conjugates.

PATIENTS AND METHODS

This retrospective, observational study included adults with HR+/HER2- mBC from the ConcertAI Patient360™ Breast Cancer dataset who initiated their first chemotherapy in the metastatic setting between January 2011 and June 2021. Treatment patterns were described; real-world overall survival, time to next treatment or death, and real-world progression-free survival were evaluated for all eligible patients and patients treated with subsequent chemotherapy. Index dates were the start date of each chemotherapy treatment.

RESULTS

Among 1545 eligible patients, 76% were white, 12% had Eastern Cooperative Oncology Group performance status ≥2, 38% had de novo mBC, and median age was 61 years (range, 52-69 years). Within the index period, capecitabine was used the most as the first chemotherapy agent and decreased in later treatments, while the use of eribulin increased between first and fourth chemotherapies. Median (95% confidence interval) real-world overall survival was 23.3 months (21.3-25.4 months) from start of first chemotherapy, time to next treatment or death was 6.5 months (5.9-7.1 months), and real-world progression-free survival was 6.9 months (6.4-7.6 months); median times from second, third, and fourth chemotherapies decreased with each additional chemotherapy treatment.

CONCLUSIONS

This real-world study demonstrates that for patients with HR+/HER2- mBC, chemotherapy provides relatively limited survival benefit which decreases with each additional chemotherapy line, and highlights the need for improved treatment options.

Incidence and Prognostic Values in Human Epidermal Growth Factor Receptor 2-Low Expression Metastatic Breast Cancer in Southeast Asian Population: A 10-Year Retrospective Study

PURPOSE

Breast cancer progression varies across molecular subtypes, and treatment options for human epidermal growth factor receptor 2 (HER2)-low expression tumors are limited compared with those of HER2 overexpression tumors. Comprehensive information regarding the epidemiology and clinical outcomes of metastatic HER2-low expression breast cancer in a Southeast Asian population is lacking.

METHODS

This retrospective cohort study was performed to analyze data from patients with de novo advanced breast cancer, including HER2 expression, tumor stage, and metastatic pattern. Statistical analyses, including chi-square tests and survival analyses, were used to compare HER2-low expression and HER2-negative groups.

RESULTS

Of the 491 patients, 21.2% had HER2-low expression, 30% had HER2 overexpression, and 50% had HER2-negative expression. Among the hormone receptor (HR)-positive patients, 34% had HER2-low expression; in the triple-negative patients, the HER2-low incidence was 20.6%. No significant differences in clinical characteristics between HER2-low and HER2-negative groups were observed, except for more HR-positive patients in the HER2-low group. HER2-low patients had a longer overall survival (OS) than HER2-negative patients (43 v 23 months; hazard ratio, 0.7; P < .001), especially in HR-positive patients. After adjusting for HR status, HER2-low patients maintained improved outcomes. HR-positive HER2-low patients showed nonsignificant OS gains compared with HR-positive HER2-negative patients, regardless of first-line chemotherapy or endocrine therapy.

CONCLUSION

This study revealed the incidence and clinical outcomes of HER2-low expression in de novo advanced breast cancer, suggesting favorable outcomes, particularly in HR-positive breast cancer. These findings may inform personalized treatment strategies. Further research into the mechanisms and implications of HER2-low expression in breast cancer is required.

The impact of human epidermal growth factor receptor-2 (low) status on the efficacy of first line cyclin-dependent kinase 4/6 inhibitors in advanced breast cancer

The fact that the human epidermal growth factor receptor 2 (HER2)-low group, historically classified as HER2 negative in breast cancer histology, benefited from HER2-targeted treatments similarly to the HER2-positive group indicates that this group has a distinct histology from the HER2-0 group. The effectiveness of cyclin-dependent kinase 4/6 inhibitors, which are the standard first-line treatment for hormone receptor-positive, HER2-negative advanced breast cancer, in this newly defined histological subgroup remains a topic of debate. In our study, we examined the impact of HER2 status on the efficacy of CDK4/6 inhibitors. Our study is a retrospective, multicenter, real-world data analysis. One hundred sixty patients were included in the study. The relationship between HER2 status and other clinical-pathological features, as well as progression-free survival, was examined. Median follow-up was 20.33 ± 0.98 months. The mPFS could not be reached. All patients exhibited positive estrogen receptor expression. Among the patients, 111 (69.4%) were categorized as HER2-0, and 49 (30.6%) as HER2-low. The 24-month progression-free survival rates were similar between HER2-0 and HER2-low patients (60.6% vs 65.3%, hormone receptor: 1.18, CI: 0.67-2.20, P = .554). We established that the mPFS achieved with cyclin-dependent kinase 4/6 inhibitors as a first-line therapy for patients with advanced breast cancer is unaffected by HER2 status.

Relationship between HER2-low status and efficacy of CDK4/6 inhibitors in advanced breast cancer: a real-world study

AIMS AND OBJECTIVES

Human epidermal growth factor receptor 2 (HER2)-low breast cancer (BC) is a new entity considered a biologically distinct subtype from HER2-zero BC. However, the importance of HER2 low expression on the activity of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) remains unclear.

METHODS/MATERIALS

We conducted a single-center retrospective study including hormone receptor-positive (HR +) /HER2- metastatic BC (mBC) patients treated with CDK4/6i plus endocrine treatment (ET) as first-line therapy. Clinical outcomes were analyzed according to HER2 expression.

RESULTS

258 women were analyzed with a median follow-up of 25.4 months; 39.9% had HER2 low, and 60.1% had HER2 zero BC. Median progression-free survival (mPFS) in the HER2-low group was 27.6 months compared with 44.3 months in the HER2-zero group (p = 0.341). In patients receiving ribociclib, the mPFS in the HER2-low group was 24.2 months compared with 53.1 months in the HER2-zero group (multivariate-adjusted HR: 1.981, 95 Cl 1.094-3.586; p = 0.024). The survival probabilities at 24, 36 and 48 months for the HER2 low and HER2 zero groups were 82%, 69%, 69% and 83%, 75% and 69%, respectively (p = 0.336). Objective response rate (p = 0.179) and disease control rate (p = 0.338) did not significantly differ between HER-2-low and HER-2-zero groups.

CONCLUSIONS

The mPFS in the Her2-zero group was almost twice that of the Her2-low group, but the difference was not statistically significant. mPFS was significantly longer in the HER2-zero group compared to the HER2-low group in patients receiving ribociclib. More prospective studies are needed to understand the actual consequences of this biomarker.

Attrition in the First Three Therapy Lines in Patients with Advanced Breast Cancer in the German Real-World PRAEGNANT Registry

Background With more effective therapies for patients with advanced breast cancer (aBC), therapy sequences are becoming increasingly important. However, some patients might drop out of the treatment sequence due to deterioration of their life status. Since little is known about attrition in the real-world setting, this study assessed attrition in the first three therapy lines using a real-world registry. Methods Patients with information available on the first three therapy lines were selected from the German PRAEGNANT registry (NCT02338167). Attrition was determined for each therapy line using competing risk analyses, with the start of the next therapy line or death as endpoints. Additionally, a simple attrition rate was calculated based on the proportion of patients who completed therapy but did not start the next therapy line. Results Competitive risk analyses were performed on 3988 1st line, 2651 2nd line and 1866 3rd line patients. The probabilities of not starting the next therapy line within 5 years after initiation of 1st, 2nd and 3rd line therapy were 30%, 24% and 24% respectively. Patients with HER2-positive disease had the highest risk for attrition, while patients with HRpos/HER2neg disease had the lowest risk. Attrition rates remained similar across molecular subgroups in the different therapy lines. Conclusion Attrition affects a large proportion of patients with aBC, which should be considered when planning novel therapy concepts that specifically address the sequencing of therapies. Taking attrition into account could help understand treatment effects resulting from sequential therapies and might help develop treatment strategies that specifically aim at maintaining quality of life.

The Modified Neo-Bioscore System for Staging Breast Cancer Treated with Neoadjuvant Therapy Based on Prognostic Significance of HER2-Low Expression

Background: Recently, the classification of HER2 status evolves from binary to ternary, and HER2-low expression may exhibit prognostic significance. We aimed to investigate whether HER2-low tumor is distinct from HER2-zero or HER2-positive tumors, and then to develop a modified staging system (mNeo-Bioscore) that incorporates HER2-low status into Neo-Bioscore. Patients and Methods: This cohort study was conducted using data from the prospective database on breast cancer patients between January 2014 and February 2019. Results: Among 259 patients enrolled in the study, the HER2-low tumor exhibited significantly lower histological grade, pathological staging and Ki-67 level than the other two groups. HER2-low patients and HER2-positive patients receiving concurrent HER2-directed therapy may have similar LRFS (p = 0.531) and OS (p = 0.853), while HER2-zero peers may have significantly worse LRFS (p = 0.006) and OS (p = 0.017). In particular, a similar trend was also found in the patients without pathological complete response after surgery. Incorporation of HER2-low status made improvement in fit: 5-year OS rate estimates ranged from 33.33% to 100% for mNeo-Bioscore vs 61.36% to 100% for Neo-Bioscore. Conclusions: This study demonstrated that HER2-low tumor may exhibit prognostic significance. The innovative mNeo-Bioscore, based on a new classification of HER2 status, may serve as a prognostic staging system superior to Neo-Bioscore.

HER2-low heterogeneity between primary and paired recurrent/metastatic breast cancer: Implications in treatment and prognosis

BACKGROUND

With the largest sample size to date, the authors' objective was to investigate the incidence of primary-to-metastatic human epidermal growth factor 2 (HER2) conversion and the predictors for such conversion. Moreover, no previous studies have evaluated the prognosis of patients who have negative HER2 expression (HER2-0) versus low HER2 expression (HER2-low) when HER2 status was assessed based on all recurrent/metastatic lesions.

METHODS

The authors included 1299 patients who had available HER2 status of primary breast tumors and paired recurrent/metastatic lesions at Fudan University Shanghai Cancer Center and West China Hospital.

RESULTS

In total, 370 patients (28.5%) experienced primary-to-metastatic HER2 conversion. Intrapatient intermetastasis spatial heterogeneity and temporal heterogeneity of HER2 were detected. When assessing HER2 based on recurrent/metastatic tumors, patients who had HER2-0 tumors had significantly shorter overall survival than those who had HER2-low tumors in the overall population and in the estrogen receptor (ER)-negative subgroup. However, when assessing HER2 based on primary tumors, there was no difference in overall survival between patients who had HER2-0 versus HER2-low tumors. Moreover, patients who had tumors that converted from HER2-0 to HER2-low had longer overall survival than those who had consistent HER2-0 status in the ER-negative subgroup. By combining four predictors (ER status, Ki67 index, biopsy site, and disease-free interval), the authors established the first prediction tool to estimate the probability of HER2-0 tumors converting to HER2-low/positive tumors.

CONCLUSIONS

Intrapatient primary-to-metastatic and intermetastatic HER2 heterogeneity were observed in this large-scale cohort study. When evaluating HER2 based on recurrent/metastatic tumors, an overall survival difference was observed between patients who had HER2-0 versus HER2-low, recurrent/metastatic breast tumors. The developed prediction tool might help clinicians screen out patients with primary HER2-0 tumors that have a high probability of HER2 status conversion and recommend them for re-biopsy, thus helping to screen out candidate patients for trastuzumab deruxtecan treatment.

Clinical, Epidemiologic, and Pathologic Significance of ERBB2-Low Expression in Breast Cancer

Importance

It is unclear whether breast cancer (BC) with low ERBB2 expression (ERBB2-low) is a distinct clinical, pathological, and epidemiological entity from BC classified as no ERBB2 expression (ERBB2-negative).

Objective

To evaluate the clinical, pathological, and epidemiologic features of BC with ERBB2-low expression compared with ERBB2-negative BC in a large population study.

Design, Setting, and Participants

This cohort study was conducted as part of the Pathways Study, a prospective, racially and ethnically diverse cohort study of women with BC enrolled between 2006 and 2013 in Kaiser Permanente Northern California (KPNC). The hematoxylin and eosin slides underwent centralized pathology review, including the percentage of tumor infiltrating lymphocytes (TILs). Breast biomarker results were extracted from pathology reports, and women were included if they had a documented ERBB2 value that was not classified ERBB2-positive. Data were analyzed from February 2023 through January 2024.

Exposure

Clinical and tumor characteristics associated with BC and ERBB2-low or ERBB2-negative status.

Main Outcome and Measures

ERBB2-low was defined as immunohistochemistry score of 1+ or 2+ (negative by in situ hybridization); ERBB2-negative was defined as immunohistochemistry score of 0+. Other data were collected by self-report or extraction from electronic health records, including BC risk factors, tumor characteristics, treatment modality, and survival outcomes, with recurrence-free survival (RFS) as the primary outcome and overall survival (OS) and BC-specific mortality (BCSM) as secondary outcomes. The clinical, pathological, and epidemiological variables were compared between ERBB2-low and ERBB2-negative BC.

Results

Of 2200 eligible patients (all female; with mean [SD] age, 60.4 [11.9] years), 1295 (57.2%) had tumors that were ERBB2-low. Hormone receptors were positive in 1956 patients (88.9%). The sample included 291 Asian patients (13.2%), 166 Black patients (7.5%), 253 Hispanic patients (11.5%), 1439 White patients (65.4%), and 51 patients (2.3%) who identified as other race or ethnicity (eg, American Indian or Alaska Native and Pacific Islander). Within the hormone receptor-negative group, patients whose tumors had ERBB2-low staining, compared with those with ERBB2-negative tumors, had better OS (hazard ratio [HR], 0.54; 95% CI, 0.33-0.91; P = .02), RFS (HR, 0.53; 95% CI, 0.30-0.95; P = .03), and BCSM (HR, 0.43; 95% CI, 0.22-0.84; P = .01). In multivariable survival analysis stratified by hormone receptor status and adjusted for key covariates, patients with ERBB2-low and hormone receptor-negative tumors had lower overall mortality (HR, 0.48; 95% CI, 0.27-0.83; P = .009), RFS (HR, 0.45; 95% CI, 0.24-0.86; P = .02), and BCSM (subdistribution HR, 0.21; 95% CI, 0.10-0.46; P < .001) compared with patients with ERBB2-negative and hormone receptor-negative tumors. Within the hormone receptor-negative subtype, patients with ERBB2-low and high TILs tumors had better survival across all 3 outcomes compared with patients with ERBB2-negative and low TILs tumors. Additionally, patients with ERBB2-low and low TILs tumors had better BCSM (subdistribution HR, 0.36; 95% CI, 0.14-0.92; P = .03).

Conclusions and Relevance

These findings suggest that there were clinical, pathological, and epidemiological differences between ERBB2-low and ERBB2-negative BC, raising the possibility that ERBB2-low might be a unique biologic entity.

Treatment Patterns and Health Outcomes among Patients with HER2 IHC0/-Low Metastatic or Recurrent Breast Cancer

Improved understanding of the biological heterogeneity of breast cancer (BC) has facilitated the development of more effective and personalized approaches to treatment. This study describes real-world evidence on treatment patterns and outcomes for a population-based cohort of patients with human epidermal growth factor receptor (HER2) IHC0 and -low BC with de novo or recurrent disease from Alberta, Canada. Patients 18+ years old diagnosed with HER2 IHC0/-low, de novo/recurrent BC from 2010 to 2019 were identified using Alberta's cancer registry. Analyses of these patients' existing electronic medical records and administrative claims data were conducted to examine patient characteristics, treatment patterns, and survival outcomes. A total of 3413 patients were included in the study, of which 72.10% initiated first line hormonal and non-hormonal systemic therapy. The 1-year overall survival (OS) was 81.09% [95% CI, 79.52-82.69]. Recurrent patients had a higher OS compared to de novo patients: 54.30 months [95% CI, 47.80-61.90] vs. 31.5 months [95% CI, 28.40-35.90], respectively. Median OS was 43.4 months [95% CI, 40.70-47.10] and 35.80 months [95% CI, 29.00-41.70] among patients with HER2-low and HER2 IHC0 cancer, respectively. The study results provide real-world evidence regarding the clinical outcomes of HER2 IHC0/-low and de novo/recurrent disease.

Prognostic implications of HER2NEU-low in metastatic breast cancer

INTRODUCTION

We explored characteristics and clinical outcomes of HER2-negative and HER2-low metastatic breast cancers using real-world data.

METHODS

We queried the National Cancer Database to identify MBC patients that were HER2-low or HER2-negative per immunohistochemical staining. A binomial regression analysis identified demographic and clinical correlates of each subtype. A Cox multivariable regression analysis (MVA) and propensity-match analysis were performed to identify correlates of survival.

RESULTS

Excluding missing data, 24,636 MBC patients diagnosed between 2008 and 2015 were identified; 27.9% were HER2-negative and 72.1% were HER2-low. There were no relevant demographic differences between the groups. HER2-low tumors were half as likely to have concomitant hormone receptor-positive status (p < 0.01). The 3-year survival rate among hormone receptor-negative patients was 33.8% for HER2-low and 32.2% for HER2-negative (p < 0.05), and 60.9% and 55.6% in HER2-low and HER2-negative cases among hormone receptor-positive patients (p < 0.05), respectively. HER2-low cases were associated with better survival on MVA (HR =0.95, 95% CI 0.91-0.99) and remained superior with propensity-matching (HR = 0.92, 95% CI 0.89-0.96). In a subset analysis isolated to hormone receptor-positive cases, HER2-low remained correlated with improved survival (HR = 0.93, 95% CI 0.89-0.98) with propensity-matched MVA. Correlates of worse survival include older age as a continuous variable (HR = 1.02, 95% CI 1.02-1.02) and Black race (HR = 1.26, 95% CI 1.20-1.32) [all p < 0.01].

CONCLUSIONS

In the largest such analysis performed to date, our study demonstrates a small but statistically significant association with improved survival for HER2-low tumors compared to HER2-negative tumors in MBC.

An Analysis of Clinical and Pathologic Features, RecurIndex Genomic Profiles, and Survival Outcomes in HER2-Low Breast Cancer

BACKGROUND

In recent years, breast cancer has become the most common cancer in the world, increasing women's health risks. Approximately 60% of breast cancers are categorized as human epidermal growth factor receptor 2 (HER2)-low tumors. Recently, antibody-drug conjugates have been found to have positive anticancer efficacy in patients with HER2-low breast cancer, but more studies are required to comprehend their clinical and molecular characteristics.

METHODS

In this study, we retrospectively analyzed the data of 165 early breast cancer patients with pT1-2N1M0 who had undergone the RecurIndex testing. To better understand HER2-low tumors, we investigated the RecurIndex genomic profiles, clinicopathologic features, and survival outcomes of breast cancers according to HER2 status.

RESULTS

First, there were significantly more hormone receptor (HR)-positive tumors, luminal-type tumors, and low Ki67 levels in the HER2-low than in the HER2-zero. Second, RI-LR (P = .0294) and RI-DR (P = .001) scores for HER2-low and HER2-zero were statistically significant. Third, within HER2-negative disease, HR-positive/HER2-low tumors showed highest ESR1, NFATC2IP, PTI1, ERBB2, and OBSL1 expressions. Fourth, results of the survival analysis showed that lower expression of HER2 was associated with improved relapse-free survival for HR-positive tumors, but not for HR-negative tumors.

CONCLUSIONS

The present study highlights the unique features of HER2-low tumors in terms of their clinical characteristics as well as their gene expression profiles. HR status may influence the prognosis of patients with HER2-low expression, and patients with HR-positive/HER2-low expression may have a favorable outcome.

Tucatinib's journey from clinical development to clinical practice: New horizons for HER2-positive metastatic disease and promising prospects for brain metastatic spread

Approximately 20% of breast cancers (BCs) overexpress human epidermal growth factor receptor 2 (HER2), a transmembrane glycoprotein with tyrosine kinase activity, encoded by ERBB2 gene. Historically, HER2 overexpression has been linked with increased disease recurrence and a worse prognosis. However, the increasing availability of different anti-HER2 compounds and combinations is progressively improving HER2-positive BC outcome, thus requiring expertise to prioritize both overall survival (OS) prolongation and quality of life, without neglecting the accessibility to further treatment lines with a low attrition rate. In this context, tucatinib, an oral tyrosine kinase inhibitor, has recently been granted approval by regulatory agencies based on evidence from the HER2CLIMB, a clinical trial which randomized patients with metastatic BC to receive trastuzumab and capecitabine with either tucatinib or placebo. A distinctive feature of this study was the inclusion of patients with new or active brain metastases (BMs) at study entry, a population traditionally excluded from clinical trials. Thus, HER2CLIMB provides the first solid evidence of an OS benefit in patients with BC and BMs, addressing a long standing unmet medical need, especially given the high incidence of central nervous system metastatic spread in patients with HER2-positive disease. This review provides an overview of the molecular and clinical landscape of tucatinib for the treatment of advanced BC. It focuses on the technological journey that drove the development of this therapeutic innovation, from preclinical data to clinical practice.

Classification of HER2-negative breast cancers by ERBB2 copy number alteration status reveals molecular differences associated with chromosome 17 gene aberrations

Background

Recently, HER2-negative breast cancers have been reclassified by protein expression into 'HER2-low' and 'HER2-zero' subgroups, but the consideration of HER2-low breast cancer as a distinct biological subtype with differing prognoses remains controversial. By contrast, non-neutral ERBB2 copy number alteration (CNA) status is associated with inferior survival outcomes compared to ERBB2 CNA-neutral breast cancer, providing an alternative approach to classification.

Methods

Here, we investigated the molecular landscape of non-metastatic HER2-negative BCs in relation to ERBB2 CNA status to elucidate biological differences. Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) and The Cancer Genome Atlas (TCGA) TCGA-BRCA datasets (n = 1875) were analyzed.

Results

Nearly two-fifths of the cohort harbored ERBB2 CNAs (39.4%), which were significantly enriched within hormone receptor-negative (56.1%) than within hormone receptor-positive BCs (35.5%; p < 0.0001). Globally, CNAs across the genome were significantly higher in ERBB2 non-neutral compared to neutral cohorts (p < 0.0001). Notably, genetic aberrations on chromosome 17 - BRCA1, NF1, TP53, MAP2K4, and NCOR1 - were widespread in the ERBB2 non-neutral cases. While chromosome 17q arm-level alterations were largely in tandem with ERBB2 CNA status, arm-level loss in chromosome 17p was prevalent regardless of ERBB2 gain, amplification, or loss. Differential gene expression analysis demonstrated that pathways involved in the cell cycle, proteasome, and DNA replication were upregulated in ERBB2 non-neutral cases.

Conclusion

Classification of HER2-negative BCs according to ERBB2 CNA status reveals differences in the genomic landscape. The implications of concurrent aberrations in other genes on chromosome 17 merit further research in ERBB2 non-neutral BCs.

Clinicopathological characteristics, evolution, treatment pattern and outcomes of hormone-receptor-positive/HER2-low metastatic breast cancer

Objective

Despite the promising efficacy of the novel antibody-drug conjugate trastuzumab deruxtecan in treating Hormone Receptor (HoR)-positive/Human Epidermal Growth Factor Receptor 2 (HER2)-low metastatic breast cancer (MBC), its categorization as a distinct entity remains disputed, as does the divergence in its endocrine and chemotherapy outcomes. This study aimed to elucidate the clinical characteristics, primary/metastatic lesion HER2 expression, and treatment outcomes of HoR-positive/HER2-low patients.

Methods

We included HoR-positive/HER2-negative MBC patients who underwent 1st and 2nd line endocrine treatment from July 2010 to October 2022 at the Fudan University Shanghai Cancer Center, comparing the clinical pathological characteristics, HER2 expression in primary/metastatic lesions, treatment, and therapeutic effects of the HER2-low and HER2-zero groups.

Results

Among the 458 HoR-positive/HER2-negative MBC patients, 54.37% (249/458) were HER2-low. The HER2-low group and the HER2-zero group had similar clinical pathological characteristics and similar progression-free survival (PFS) of 1st and 2nd line endocrine treatment (median PFS: 8.05 months vs 10.12 months, p=0.114, HR 1.257, 95% CI 0.771 to 1.028). The PFS of the HER2-low and HER2-zero groups was also similar, treated with different endocrine drugs (including aromatase inhibitors, tamoxifen/toremifene, fulvestrant, palbociclib, and everolimus). However, the HER2-low group had significantly shorter PFS during 1st and 2nd line chemotherapy compared to the HER2-zero group (median PFS: 8.64 vs 9.03 months, p=0.027, HR 0.841, 95% CI 0.721-0.980). Additionally, 41.18% (63/153) of patients exhibited a change in HER2 expression between primary and metastatic lesions. Notably, patients whose HER2 status changed from zero to low expression had significantly prolonged PFS during chemotherapy compared to those who maintained low HER2 expression (median PFS: 14.29 vs 11.27 months, p=0.048, HR 0.597, 95% CI 0.358-0.996).

Conclusion

In HoR-positive MBC, patients with low and zero HER2 expression have similar clinical characteristics and respond similarly to endocrine treatment, but the chemotherapy effect is worse in the HER2-low patients. Moreover, the transformation of HER2 status from primary to metastatic lesions may have potential influence on chemotherapy outcomes. Therefore, the expression and heterogeneity of HER2 should be considered in clinical decisions.

Tumor characteristics and survival rate of HER2-low breast cancer patients: a retrospective cohort study

HER2 is an important prognostic marker in breast cancer (BC) patients, which also plays a crucial role in their therapeutic plan. Consequently, a great desire is to thoroughly assess the patients based on their HER2 status. In the current study, we aimed to evaluate HER2-low breast cancer as a new subtype in the standard classification of BC patients and review its characteristics and survival rate in a tertiary center in Iran. We retrospectively evaluated disease-free survival (DFS), overall survival (OS), and clinicopathological characteristics of BC patients referred to the Cancer Research Center in Tehran, Iran from 1991 to 2022. Patients' clinical characteristics, including HER2 status, which is classified as HER2-low, HER2-positive, or HER2-negative, were obtained from prospectively maintained registries. Among the total 3582 recruited patients, 60.2%, 13.6%, and 26.2% were HER2-negative, HER2-low, and HER2-positive, respectively. HER2-positive patients showed a significantly higher Hazard Ratio (HR) for DFS (HR 1.44, 95% CI 1.01-2.05) and OS (HR 2.05, 95% CI 1.31-3.20), compared to HER2-low. Moreover, HER2-low and HER2-negative were found to show the same proportion of high-grade tumors (28 and 28.4%), while 40% of the HER2-positive tumors were high-grade. Accordingly, HER2-low patients had a lower metastasis risk than the others (P-value = 0.01). The Ki67 percentage was significantly lower in the HER2-low group compared to the HER2-positive (P-value < 0.001). HER2-low, a new subtype of HER2-status classification with distinct biological and clinicopathological traits, represented the highest survival rate and less invasive characteristics. This difference was statistically significant when compared to HER2-positive, but not when compared to HER2-negative.Research registration unique identifying number: NCT05754047.

Analysis of the association of HER-2 low carcinomas and PAM50 assay in hormone receptor positive early-stage breast cancer

BACKGROUND

HER2-low has emerged as a new predictive biomarker in metastatic breast cancer. However, its prognostic value in early-stage carcinomas needs to be revisited. We aimed to evaluate the association of HER2-low carcinomas with PAM50 risk groups combined with clinicopathological variables in early breast cancer.

METHODS

We conducted a retrospective analysis of 332 patients with early-stage breast cancer that underwent PAM50 signature analysis between 2015 and 2021at Hospital Universitario 12 de Octubre (Madrid, Spain). Clinical and pathological variables were collected from medical records. After adjusting for potential confounders, we estimated Odds Ratio (OR) and 95% confidence interval for high-risk PAM50 subgroup, comparing HER2-low versus HER2-zero carcinomas by multivariable logistic regression. P values below 0.05 were deemed statistically significant.

RESULTS

192 (57%) patients were classified as HER2-low carcinomas. Median follow-up was 34 months. Adjusted OR for high-risk PAM50 when comparing HER2-low versus HER2-zero carcinomas was 1.31 (95% CI: 0.75-2.30, p = 0.33). The multivariable model detected significant associations for Ki-67% (≥20% vs. <20%: OR = 4.03, 95% CI: 2.15-7.56, p < 0.001), T staging category (T2/T3 vs. T1: OR = 3.44, 95% CI: 1.96-6.04, p < 0.001), progesterone receptor (PR ≥ 20% vs. <20%: OR = 0.44, 95% CI: 0.23-0.83, p = 0.01), nodal staging category (N+ vs. N0: OR = 3.8, 95% CI: 1.89-7.62, p < 0.001) and histological grade (grade 2 vs. 1: OR = 2.41, 95% CI: 1.01-5.73, p = 0.04; grade 3 vs 1: OR = 5.40, 95%CI: 1.98-14.60, p = 0.001).

CONCLUSIONS

In this early-stage breast cancer cohort, HER2-low was not associated with a high-risk PAM50 compared to HER2-zero carcinomas. Ki-67 ≥ 20%, T2/T3, histological grade 2/3, N+ and PR<20% were significantly associated to a high-risk PAM50.

A review of treatment options in HER2-low breast cancer and proposed treatment sequencing algorithm

The expansion of the spectrum of human epidermal growth factor receptor 2 (HER2)-status to HER2-low, defined as HER2 expression of 1+ by immunohistochemistry (IHC) or 2+ by IHC without gene amplification, has made a major impact in the field of oncology. The HER2-low expression has emerged as a targetable biomarker, and anti-HER2 antibody-drug conjugate trastuzumab deruxtecan has shown significant survival benefit in pretreated metastatic HER2-low breast cancer (BC). With these recent data, the treatment algorithm for hormone receptor-positive and triple-negative BC needs to be reconsidered, as approximately half of these BCs are HER2-low. Although there are different therapeutic agents for hormone receptor-positive and hormone receptor-negative HER2-low BCs, there is no consensus regarding the sequencing of these agents. In this article, the treatment options for HER2-low BC are enumerated and a treatment sequencing algorithm based on the current clinical evidence proposed.

Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer

PURPOSE.—

To update the American Society of Clinical Oncology-College of American Pathologists (ASCO-CAP) recommendations for human epidermal growth factor receptor 2 (HER2) testing in breast cancer. An Update Panel is aware that a new generation of antibody-drug conjugates targeting the HER2 protein is active against breast cancers that lack protein overexpression or gene amplification.

METHODS.—

The Update Panel conducted a systematic literature review to identify signals for updating recommendations.

RESULTS.—

The search identified 173 abstracts. Of 5 potential publications reviewed, none constituted a signal for revising existing recommendations.

RECOMMENDATIONS.—

The 2018 ASCO-CAP recommendations for HER2 testing are affirmed.

DISCUSSION.—

HER2 testing guidelines have focused on identifying HER2 protein overexpression or gene amplification in breast cancer to identify patients for therapies that disrupt HER2 signaling. This update acknowledges a new indication for trastuzumab deruxtecan when HER2 is not overexpressed or amplified but is immunohistochemistry (IHC) 1+ or 2+ without amplification by in situ hybridization. Clinical trial data on tumors that tested IHC 0 are limited (excluded from DESTINY-Breast04), and evidence is lacking that these cancers behave differently or do not respond similarly to newer HER2 antibody-drug conjugates. Although current data do not support a new IHC 0 versus 1+ prognostic or predictive threshold for response to trastuzumab deruxtecan, this threshold is now relevant because of the trial entry criteria that supported its new regulatory approval. Therefore, although it is premature to create new result categories of HER2 expression (eg, HER2-Low, HER2-Ultra-Low), best practices to distinguish IHC 0 from 1+ are now clinically relevant. This update affirms prior HER2 reporting recommendations and offers a new HER2 testing reporting comment to highlight the current relevance of IHC 0 versus 1+ results and best practice recommendations to distinguish these often subtle differences. Additional information is available at www.asco.org/breast-cancer-guidelines.

Clinical characteristics, tumor-infiltrating lymphocytes, and prognosis in HER2-low breast cancer: A comparison study with HER2-zero and HER2-positive disease

INTRODUCTION

HER2-low breast cancer is a gradually recognized and unexplored group of diseases. We aimed to investigate the clinical and prognosis features and to identify the role of stromal tumor-infiltrating lymphocytes (sTILs) in this population.

METHODS

Consecutive primary breast cancer patients treated between January 2009 to June 2013 were retrospectively reviewed. HER2-low was defined as immunohistochemistry (IHC) 1+, or 2+ and fluorescence in situ hybridization (FISH) negative. sTILs were scored following the international guidelines. Clinicopathologic features and survival were compared according to HER2 and sTILs category.

RESULTS

A total of 973 breast cancer patients were enrolled, including 615 (63.2%) HER2-low patients. HER2-low patients shared more similarity with HER2-0 cases in clinicopathological features. sTILs in HER2-Low patients was comparable to HER2-0 patients (p = 0.064), both significantly lower than HER2-positive ones (p < 0.001). Meanwhile, tumors with sTILs ≥50% accounted for the least proportion of HER2-low cases (p < 0.001). HER2 status had no significant influence on recurrence-free survival (RFS, p = 0.901) in the whole population. However, in the estrogen receptor (ER)-negative subgroup, HER2-low was related to worse RFS (p = 0.009) and OS (p = 0.001) compared with HER2-positive ones. sTILs increment was an independent favorable prognostic factor in the whole (OS, p = 0.003; RFS, p = 0.005) and HER2-low population (OS, p = 0.007; RFS, p = 0.009) after adjusted to clinicopathological parameters.

CONCLUSIONS

HER2-low patients shared similar clinicopathological features with HER2-0 rather than HER2-positive cases and had relatively low sTILs. ER-negative/HER2-low patients had significantly inferior survival. sTILs increment was independently associated with favorable survival in the HER2-low group, suggesting a potential benefit from a novel treatment strategy.

Comparisons of clinical characteristics, prognosis, epidemiological factors, and genetic susceptibility between HER2-low and HER2-zero breast cancer among Chinese females

BACKGROUND

Traditional human epidermal growth factor receptor 2 (HER2)-negative breast cancer (BC) is recommended to be divided into HER2-low and HER2-zero subtypes due to different prognosis. However, few studies investigated their differences in clinical characteristics and prognosis among Chinese HER2-negative BC and their stratified differences by hormone receptor (HR), while fewer studies investigated their differences in epidemiological factors and genetic susceptibility.

METHODS

A total of 11,911 HER2-negative BC were included to compare the clinical characteristics and prognosis between HER2-zero and HER2-low BC, and 4227 of the 11,911 HER2-negative BC were further compared to 5653 controls to investigate subtype-specific epidemiological factors and single nucleotide polymorphisms(SNPs).

RESULTS

Overall, 64.2% of HER2-negative BC were HER2-low BC, and the stratified proportions of HER2-low BC were 61.9% and 75.2% for HR-positive and HR-negative BC, respectively. Compared to HER2-zero BC, HER2-low BC among HR-positive BC showed younger age at diagnosis, later stage, poorer differentiation, and higher Ki-67, while elder age at diagnosis and lower mortality were observed for HER2-low BC among HR-negative BC (all p values <0.05). Compared to healthy controls, both HER2-low and HER2-zero BC are associated with similar epidemiological factors and SNPs. However, stronger interaction between epidemiological factors and polygenic risk scores were observed for HER2-zero BC than HER2-low BC among either HR-positive [odds ratios: 10.71 (7.55-15.17) and 8.84 (6.19-12.62) for the highest risk group compared to the lowest risk group] or HR-negative BC [7.00 (3.14-15.63) and 5.70 (3.26-9.98)].

CONCLUSIONS

HER2-low BC should deserve more attention than HER2-zero BC, especially in HR-negative BC, due to larger proportion, less clinical heterogeneity, better prognosis, and less susceptibility to risk factors.

Analysis of clinical features, genomic landscapes and survival outcomes in HER2-low breast cancer

BACKGROUND

Novel human epidermal growth factor receptor 2 (HER2)-directed antibody-drug conjugates prompt the identification of the HER2-low subtype. However, the biological significance of HER2-low expression in breast cancer is unclear.

METHODS

Clinical and genomic data of 579 metastatic breast cancer patients were reviewed from our next-generation sequencing (NGS) database and genomic analysis of early breast cancer patients from TCGA was also analyzed.

FINDINGS

First, the clinicopathological characteristics of HER2-low patients were profoundly influenced by HR status and no difference of prognosis was observed between HER2-low and HER2-zero patients when paired by HR status, but notably HER2-low patients showed similar metastatic patterns to HER2-positive patients in the HR-positive (HR+ ) subgroup, with more brain and initial lung metastases and more cases of de novo stage IV breast cancer than HER2-zero patients. Second, among patients with primary HER2-low or HER2-zero tumors, the discordance of HER2 status between primary and metastatic tumors was significant, with 48.4% of patients with HER2-zero primary tumors exhibiting HER2-low phenotype in metastatic tumors in the HR+ subgroup. Third, within HR+ and HR-negative subtypes, HER2-low and HER2-zero tumors showed no substantial differences in mutation alterations and copy number variations. Forth, germline BRCA2 mutations were observed only in HER2-low patients in our NGS database, especially in HR+ HER2-low tumors. Finally, three molecular subtypes based on genomic alterations in HER2-low breast cancer were identified, which provided novel insights into heterogeneity in HER2-low breast cancer.

CONCLUSIONS

After correcting for HR expression, only marginal differences in clinical and molecular phenotypes were determined between HER2-low and HER2-zero breast cancer. Therefore, HER2-low breast cancer is insufficient to be defined as a distinct molecular entity, but rather a heterogenous disease.

HER2-Low Breast Cancer: Incidence, Clinicopathologic Features, and Survival Outcomes From Real-World Data of a Large Nationwide Cohort

Patients with breast cancer (BC) with low levels of human epidermal growth factor receptor 2 (HER2) expression (HER2-low) could benefit from novel antibody-drug conjugates. However, there is conflicting information regarding the characteristics of HER2-low BC and its outcome. We assessed the clinicopathologic characteristics and outcomes of HER2-low BC using real-world data from the Dutch National Pathology Registry. This retrospective study incorporated all patients with primary invasive BC, without neoadjuvant therapy, reported in the Dutch National Pathology Registry synoptic reporting module between 2014 and 2022. HER2 status was categorized as HER2-0 (defined as an immunohistochemistry score of 0 according to the current American Society of Clinical Oncology/College of American Pathologists guidelines) or HER2-low (immunohistochemistry score 1+ or 2+ without amplification). Clinicopathologic characteristics and overall survival of HER2-low BC were compared with HER2-0, adjusted for estrogen receptor (ER) status. We included 65,035 patients with BC, resulting in 69,424 tumors. The proportion of HER2-low BC was 62% in the ER+ cohort and 38% in the ER- cohort. A substantial number of patients had a different HER2 category between the needle biopsy and the corresponding surgical resection (28%) or among multiple tumors (28%). After multivariable logistic analysis, HER2-low tumors were significantly associated with histologic subtype, a higher ER, and lower progesterone receptor expression in the ER+ cohort, whereas within the ER-cohort, HER2-low tumors were associated with a lower tumor grade. However, the absolute differences were limited, and there was no significant difference in overall survival between HER2-low and HER2-0 tumors within the ER+ or ER- cohort. The classification of HER2 expression (HER2-0 vs HER2-low) varies between biopsies and corresponding resection specimens and within multiple tumors in the same patient, which could affect clinical decision making in case only HER2-low cases are eligible for novel HER2-targeting agents. The limited follow-up time and the lack of substantial clinicopathologic differences between HER2-low and HER2-0-cases could explain the lack of differences in overall survival.

HER2-Low Breast Cancer: a New Subtype?

OPINION STATEMENT

Breast cancer (BC) guidelines subdivide the disease into three main groups, namely hormone receptor (HR)-positive HER2-negative, HER2-positive, and triple-negative BC (TNBC). The natural history of the HER2-positive subtype has changed since the introduction of HER-targeted therapies, which demonstrated benefit only in case of HER2 overexpression (IHC, score 3+) or gene amplification. Such observation may depend on direct drug inhibition of HER2 downstream signaling, which is needed for survival and proliferation in HER2-addicted BC. Clinically focused categories cannot comprehensively describe biology, as almost half of the currently defined HER2-negative BCs show some degree of IHC expression and have been recently renamed as HER2-low. Why? As technological breakthroughs enable the synthesis of antibody-drug conjugates (ADCs), target antigens may be viewed not only as a biological switch to be turned on-off by targeted drugs but also as an anchor for ADC docking and tethering. As trastuzumab deruxtecan (T-DXd) has already proven in the clinical trial DESTINY-Breast04, even fewer HER2 available receptors on cancer cells may be sufficient for a clinical benefit. So, for HR-negative HER2-low subtype (~40% of TNBCs), though only 58 patients had been enrolled in DESTINY-Breast04, the observed benefit, together with the dismal prognosis of TNBC, warrants the use of T-DXd. Notably, another topoisomerase-based ADC, sacituzumab govitecan, has already been granted approval for pretreated TNBC (ASCENT). As no head-to-head comparison has been performed, the choice relies on regulatory approvals at the time of patient assessment, critical appraisal of available evidence, and careful evaluation of possible cross-resistance with sequential use of ADCs. As for HR-positive HER2-low disease (~60% of HR-positive tumors), DESTINY-Breast04 provides solid evidence for T-DXd prioritization in either second or third treatment lines. Although the remarkable activity observed in this setting favorably compares with outcomes observed in treatment-naive patients, the ongoing DESTINY-Breast06 will clarify the role of T-DXd in this population.

The association between HER2-low expression and prognosis of breast cancer: a systematic review and meta-analysis

Background

The use of antibody-drug conjugates for the treatment of advanced-stage human epidermal growth factor receptor 2 (HER2)-low expression in breast cancer (BC) has shown prominent curative effects, which has led to increased academic interest. However, the role of HER2-low expression in the prognosis of BC remains controversial.

Methods

We conducted a systematic search of the PubMed, Embase, and Cochrane library databases and several oncology conferences until 20 September 2022. We used fixed- and random-effects models to calculate odds ratio (OR) or hazard ratio (HR) with 95% confidence interval (CI) for overall survival (OS), disease-free survival (DFS), progression-free survival (PFS), and pathological complete response (pCR) rates.

Results

Overall, 26 studies encompassing 677,248 patients were included in the meta-analysis. Patients with HER2-low BC showed significantly better OS than those with HER2-zero BC in the overall population (HR = 0.90; 95% CI: 0.85-0.97) and hormone receptor-positive population (HR = 0.98; 95% CI: 0.96-0.99), whereas no significant difference was observed in the OS of the hormone receptor-negative population (p > 0.05). In addition, there was no significant difference in the DFS of the overall and hormone receptor-negative population (p > 0.05), but better DFS than those with HER2-zero BC in the hormone receptor-negative population (HR = 0.96; 95% CI: 0.94-0.99). There was also no significant difference in the PFS of the overall population, hormone receptor-positive, and hormone receptor-negative population (p > 0.05). Patients with HER2-low BC had a lower pCR rate after neoadjuvant treatment than those with HER2-zero BC.

Conclusions

Compared to patients with HER2-zero BC, those with HER2-low BC had better OS in the overall population and hormone receptor-positive population, DFS in hormone receptor-positive population and lower pCR in the overall population. The biological differences between HER2-low and HER2-zero BCs, particularly in hormone receptor-positive patients, and the relationship between HER2-low expression status and prognosis need to be explored further.

Influence of HER2 expression on prognosis in metastatic triple-negative breast cancer-results from an international, multicenter analysis coordinated by the AGMT Study Group

BACKGROUND

Triple-negative breast cancer (TNBC) is associated with poor prognosis, and new treatment options are urgently needed. About 34%-39% of primary TNBCs show a low expression of human epidermal growth factor receptor 2 (HER2-low), which is a target for new anti-HER2 drugs. However, little is known about the frequency and the prognostic value of HER2-low in metastatic TNBC.

PATIENTS AND METHODS

We retrospectively included patients with TNBC from five European countries for this international, multicenter analysis. Triple-negativity had to be shown in a metastatic site or in the primary breast tumor diagnosed simultaneously or within 3 years before metastatic disease. HER2-low was defined as immunohistochemically (IHC) 1+ or 2+ without ERBB2 gene amplification. Survival probabilities were calculated by the Kaplan-Meier method, and multivariable hazard ratios (HRs) were estimated by Cox regression models.

RESULTS

In total, 691 patients, diagnosed between January 2006 and February 2021, were assessable. The incidence of HER2-low was 32.0% [95% confidence interval (CI) 28.5% to 35.5%], with similar proportions in metastases (n = 265; 29.8%) and primary tumors (n = 425; 33.4%; P = 0.324). The median overall survival (OS) in HER2-low and HER2-0 TNBC was 18.6 and 16.1 months, respectively (HR 1.00; 95% CI 0.83-1.19; P = 0.969). Similarly, in multivariable analysis, HER2-low had no significant impact on OS (HR 0.95; 95% CI 0.79-1.13; P = 0.545). No difference in prognosis was observed between HER2 IHC 0/1+ and IHC 2+ tumors (HR 0.89; 95% CI 0.69-1.17; P = 0.414).

CONCLUSIONS

In this large international dataset of metastatic TNBC, the frequency of HER2-low was 32.0%. Neither in univariable nor in multivariable analysis HER2-low showed any influence on OS.

How I treat HER2-low advanced breast cancer

INTRODUCTION

Targeting low levels of human receptor epidermal growth factor 2 (HER2) expression has reshaped the treatment paradigm for half of the patients with advanced breast cancer. HER2-low is currently defined as a HER2 immunohistochemical expression of 1+ or 2+ without amplification by in-situ hybridization. Until recently, HER2-targeted agents were ineffective in treating patients with HER2-low disease.

AREAS COVERED

In this narrative review, we summarize the current management of HER2-low breast cancer. We highlight the findings of the DESTINY-Breast 04 phase 3 trial, which confirmed the efficacy of trastuzumab-deruxtecan (T-DXd) for the treatment of patients with advanced, pretreated HER2-low breast cancer. We also discuss how to implement this new treatment option in treatment algorithms of hormone receptor (HR)-positive and triple-negative tumors, as well as how to optimally manage selected toxicities of T-DXd.

EXPERT OPINION

T-DXd is currently the standard of care for patients with advanced, pretreated, HER2-low breast cancer. Based on the design of the DESTINY-Breast04 trial, the current optimal place in treatment algorithms is after the first line of chemotherapy, both in HR-positive and triple-negative breast cancer. Up to 10-15% of the patients receiving T-DXd are expected to develop interstitial lung disease, which in 1-2% of the cases can be fatal. Adequate monitoring and prompt management are required to minimize the impact of ILD and to safely implement T-DXd in clinical practice.

Biology and Treatment of HER2-Low Breast Cancer

Current guidelines recommend a dichotomous classification of HER2 as either positive or negative, to guide clinicians in treatment decisions. Until now, only patients with HER2-positive breast cancer (BC) had been demonstrated to derive clinical benefit from anti-HER2 therapies. However, novel ADCs have recently emerged, with activity in the large population of patients with HER2-low-expressing BC. Although it remains unclear whether HER2-low BC represents a distinct entity, given the therapeutic implication its crucial to accurately distinguish HER2-low from HER2-0 BC. Efforts are needed to standardize HER2 testing in BC and to introduce more sensitive assays to better discriminate HER2 levels.

Pathological complete response, long-term outcomes, and recurrence patterns in HER2-low versus HER2-zero breast cancer after neoadjuvant chemotherapy

BACKGROUND

The interest in HER2-low breast cancer (BC) has increased in recent years with the development of novel anti-HER2 antibody-drug conjugates. Here, we investigated the clinical outcomes and relapse patterns of patients with HER2-low or -zero BCs in an Asian population.

METHODS

We retrospectively identified HER2-low or -zero BC patients with stage I-III tumours who were treated with neoadjuvant chemotherapy and underwent curative surgery, between 2014 and 2018 at Asan Medical Center, Seoul, Korea.

RESULTS

A total of 818 and 754 HER2-zero and HER2-low BC patients, respectively, were consecutively included in this analysis. The HER2-low group had more hormone receptor [HR]-positive patients (81% versus 56%, P < 0.001). The HER2-zero group had a higher proportion of patients who achieved pathological complete response (pCR) (14.7% versus 9.8%, P = 0.003); however, no significant differences of pCR rate by HER2 status were identified in the HR-positive (P = 0.4) and HR-negative groups (P = 0.3) when analysed separately. The HER2-low BC cases had higher 5-year overall survival (OS) and disease-free survival (DFS) rates (P < 0.001 for OS; P = 0.002 for DFS); however, no differences were observed in terms of OS and DFS by HER2 status in the HR-positive group (P = 0.21 for OS and P = 0.66 for DFS).

CONCLUSIONS

Our current findings do not support that HER2-low BC had different biology and clinical features compared to HER2-zero BC in patients who treated with neoadjuvant chemotherapy. However, the prognostic impact of HER2-low status in BC remains controversial; thus warranting further research.

HER2-Low Status Does Not Affect Survival Outcomes of Patients with Metastatic Breast Cancer (MBC) Undergoing First-Line Treatment with Endocrine Therapy plus Palbociclib: Results of a Multicenter, Retrospective Cohort Study

Background: Approximately 45–50% of breast cancers (BCs) have a HER2 immunohistochemical score of 1+ or 2+ with negative in situ hybridization, defining the “HER2-low BC” subtype. No anti-HER2 agents are currently approved for this subgroup in Europe, where treatment is still determined by HR expression status. In this study, we investigated the prognostic significance of HER2-low status in HR+/HER2- metastatic BC (MBC) patients treated with endocrine therapy (ET) plus palbociclib as first line. Methods: We conducted a retrospective study including 252 consecutive HR+/HER2- MBC patients who received first-line ET plus palbociclib at six Italian Oncology Units between March 2016 and June 2021. The chi-square test was used to assess differences in the distribution of clinical and pathological variables between the HER-0 and HER2-low subgroups. Survival outcomes, progression-free survival (PFS) and overall survival (OS), were calculated by the Kaplan–Meier method, and the log-rank test was performed to estimate the differences between the curves. Results: A total of 165 patients were included in the analysis: 94 (57%) and 71 (43%) patients had HER2-0 and HER2-low disease, respectively. The median age at treatment start was 64 years. No correlation between patients and tumor characteristics and HER2 status was found. Median PFS (mPFS) for the entire study cohort was 20 months (95% CI,18–25 months), while median OS (mOS) was not reached at the time of analysis. No statistically significant differences, in terms of PFS (p = 0.20) and OS (p = 0.1), were observed between HER2-low and HER2-0 subgroups. Conclusions: In our analysis, HR+ MBC patients with low HER2 expression who received first-line treatment with ET plus Palbociclib reported no statistically different survival outcomes compared to HER2-0 patients. Further prospective studies are needed to confirm the clinical role of HER2 expression level.

HER2-low inflammatory breast cancer: Clinicopathologic features and prognostic implications

BACKGROUND

HER2)-low expression is a predictive biomarker for novel anti-HER2 antibody-drug conjugates. However, little is known about its clinical significance in inflammatory breast cancer (IBC).

METHODS

Patients diagnosed with HER2-negative IBC between December 1999 and December 2020 were identified from the Dana-Farber Cancer Institute IBC registry. Patients were divided into HER2-low (IHC 1+ or 2+/ISH-) and HER2-zero (IHC 0), comparing clinicopathologic features and disease outcomes between the two subgroups.

RESULTS

The study included 276 patients. Among patients with stage III (n = 209) and stage IV (n = 67) IBC, 54% and 39% had HER2-low tumours, respectively. Oestrogen receptor (ER)-expressing tumours were more common in patients with HER2-low versus HER2-zero stage III IBC (65% versus 38%, p < 0.01). Among stage III patients undergoing surgery (n = 182), pathologic complete response (pCR) rates were higher for HER2-zero versus HER2-low IBC (11% versus 6%, OR: 1.8, 95%CI:0.6-5.3), but minimal differences persisted when separately analysing pCR by ER status. Similar invasive disease-free survival (iDFS) outcomes were observed among ER-positive HER2-zero versus HER2-low IBC (48-month iDFS: 63% versus 63%, HR: 1.10, 95%CI:0.57-2.13) and ER-negative HER2-zero versus HER2-low IBC (48-month iDFS: 28% versus 25%, HR: 1.19, 95%CI:0.69-2.04). Differences in overall survival (OS) were small, both among ER-positive HER2-zero versus HER2-low IBC (48-month OS: 80% versus 81%, HR: 0.82, 95%CI:0.39-1.73) and ER-negative HER2-zero versus HER2-low IBC (48-month OS: 34% versus 47%, HR: 1.34, 95%CI: 0.74-2.41).

CONCLUSIONS

Marginal differences in clinicopathologic features and outcomes were observed in HER2-low versus HER2-zero IBC when controlling for ER status, not supporting the definition of HER2-low as a distinct subtype of IBC.

Update Breast Cancer 2022 Part 4 - Advanced-Stage Breast Cancer

For the treatment of patients with advanced HER2-negative hormone receptor-positive breast cancer, several substances have been introduced into practice in recent years. In addition, other drugs are under development. A number of studies have been published over the past year which have shown either an advantage for progression-free survival or for overall survival. This review summarizes the latest results, which have been published at current congresses or in specialist journals, and classifies them in the clinical treatment context. In particular, the importance of therapy with CDK4/6 inhibitors - trastuzumab deruxtecan, sacituzumab govitecan and capivasertib - is discussed. For trastuzumab deruxtecan, an overall survival benefit in HER2-negative breast cancer with low HER2 expression (HER2-low expression) was reported in the Destiny-Breast-04 study. Similarly, there was an overall survival benefit in the FAKTION study with capivasertib. The lack of overall survival benefit for palbociclib in the first line of therapy raises the question of clinical classification.

Comparison of Management and Outcomes in ERBB2-Low vs ERBB2-Zero Metastatic Breast Cancer in France

IMPORTANCE

ERBB2-low (ie, ERBB2 immunohistochemistry score of 1+ or 2+ in the absence of ERBB2 gene amplification) breast cancer (BC) is a new entity, with emerging dedicated treatments. Little is known about its prognosis and response to conventional therapy compared with ERBB2-zero breast tumors (ie, those with an immunohistochemistry score of 0).

OBJECTIVE

To compare the outcomes for patients with ERBB2-low metastatic BC (MBC) with those of patients with ERBB2-zero MBC.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study was conducted from the Epidemiological Strategy and Medical Economics MBC platform and included patients with MBC treated between 2008 and 2016 in 18 French comprehensive cancer centers. The data analysis was conducted from July 16, 2020, to April 1, 2022.

MAIN OUTCOMES AND MEASURES

The main outcome was overall survival (OS), and the secondary outcome was progression-free survival under first-line treatments (PFS1).

RESULTS

The median (range) age was 60.0 (22.0-103.0) years. Among 15 054 patients with MBC, 4671 (31%) had ERBB2-low MBC and 10 383 (69%) had ERBB2-zero MBC. The proportion of ERBB2-low cancers was higher among patients with hormone receptor-positive MBC than those with hormone receptor-negative disease (4083 patients [33.0%] vs 588 patients [21.0%]). With a median follow-up of 49.5 months (95% CI, 48.6-50.4 months), the median OS of the ERBB2-low group was 38.0 months (95% CI, 36.4-40.5 months) compared with 33.9 months (95% CI, 32.9-34.9 months) for the ERBB2-zero group (P < .001). After adjustment for age, visceral metastases, number of metastatic sites, de novo disease, period of care, and hormone receptor status, patients with ERBB2-low MBC had slightly better OS compared with patients with ERBB2-zero MBC (adjusted hazard ratio, 0.95; 95% CI, 0.91-0.99; P = .02). In contrast, PFS1 did not differ by ERBB2 status (adjusted hazard ratio, 0.99; 95% CI, 0.95-1.02; P = .45). No significant differences in OS and PFS1 were observed in multivariate analyses by hormone receptor status and types of frontline treatment.

CONCLUSIONS AND RELEVANCE

In this large cohort study, patients with ERBB2-low MBC had a slightly better OS than those with completely ERBB2-zero tumors, but identical PFS1, which could help guide treatment selection.

Clinicopathological Characteristics and Prognosis of HER2-Low Early-Stage Breast Cancer: A Single-Institution Experience

Background

Human epidermal growth factor 2 (HER2)-low breast cancer, which is defined as HER2 1+ or 2+ in immunohistochemistry without gene amplification, accounts for a considerable part of all breast cancers. However, it remains controversial whether HER2-low breast cancer is a distinct entity. Our aim was to compare the clinicopathological features and survival outcomes between HER2-zero and HER2-low early breast cancer.

Methods

The study was a retrospective analysis that enrolled 1,039 patients with available HER2 expression data in a single institute from 2013 to 2014, of whom 262 HER2-positive patients were excluded from the subsequent analysis. The remaining patients were divided into HER2-zero and HER2-low groups. Each group was further categorized into a hormone receptor (HR)-positive and an HR-negative subgroup. Clinicopathological characteristics were collected and compared between HER2-zero and HER2-low groups. The primary endpoint was disease-free survival (DFS) and overall survival (OS), which were analyzed using the Kaplan–Meier method with log-rank test, landmark analysis, and Cox proportional hazards model.

Results

A total of 777 non-HER2-positive patients were included in this analysis, of whom 126, 552, 53, and 46 patients were HR-positive/HER2-zero, HR-positive/HER2-low, HR-negative/HER2-zero, and HR-negative/HER2-low, respectively. No significant difference in DFS and OS was detected between the HER2-zero group and the HER2-low group when paired by HR status. Landmark analysis with a time point set at 5 years indicated that HR-positive/HER2-low patients had a better DFS compared with HR-positive/HER2-zero patients after 5 years (p = 0.0047). HER2-low status was an independent prognostic factor for DFS after 5 years [hazard ratio (HR) 0.31, 95% confidence interval (CI) 0.13–0.75, p = 0.01].

Conclusion

The clinicopathological characteristics and prognosis of HER2-zero and HER2-low breast cancer were similar regardless of HR status. Patients with HR-positive/HER2-low tumors tended to have a better DFS than their HR-positive/HER2-zero counterparts after 5 years.

HER2 expression, copy number variation and survival outcomes in HER2-low non-metastatic breast cancer: an international multicentre cohort study and TCGA-METABRIC analysis

BACKGROUND

HER2-low breast cancer (BC) is currently an area of active interest. This study evaluated the impact of low expression of HER2 on survival outcomes in HER2-negative non-metastatic breast cancer (BC).

METHODS

Patients with HER2-negative non-metastatic BC from 6 centres within the Asian Breast Cancer Cooperative Group (ABCCG) (n = 28,280) were analysed. HER2-low was defined as immunohistochemistry (IHC) 1+ or 2+ and in situ hybridization non-amplified (ISH-) and HER2-zero as IHC 0. Relapse-free survival (RFS) and overall survival (OS) by hormone receptor status and HER2 IHC 0, 1+ and 2+ ISH- status were the main outcomes. A combined TCGA-BRCA and METABRIC cohort (n = 1967) was also analysed to explore the association between HER2 expression, ERBB2 copy number variation (CNV) status and RFS.

RESULTS

ABCCG cohort median follow-up was 6.6 years; there were 12,260 (43.4%) HER2-low BC and 16,020 (56.6%) HER2-zero BC. The outcomes were better in HER2-low BC than in HER2-zero BC (RFS: centre-adjusted hazard ratio (HR) 0.88, 95% CI 0.82-0.93, P < 0.001; OS: centre-adjusted HR 0.82, 95% CI 0.76-0.89, P < 0.001). On multivariable analysis, HER2-low status was prognostic (RFS: HR 0.90, 95% CI 0.85-0.96, P = 0.002; OS: HR 0.86, 95% CI 0.79-0.93, P < 0.001). These differences remained significant in hormone receptor-positive tumours and for OS in hormone receptor-negative tumours. Superior outcomes were observed for HER2 IHC1+ BC versus HER2-zero BC (RFS: HR 0.89, 95% CI 0.83-0.96, P = 0.001; OS: HR 0.85, 95% CI 0.78-0.93, P = 0.001). No significant differences were seen between HER2 IHC2+ ISH- and HER2-zero BCs. In the TCGA-BRCA and METABRIC cohorts, ERBB2 CNV status was an independent RFS prognostic factor (neutral versus non-neutral HR 0.71, 95% CI 0.59-0.86, P < 0.001); no differences in RFS by ERBB2 mRNA expression levels were found.

CONCLUSIONS

HER2-low BC had a superior prognosis compared to HER2-zero BC in the non-metastatic setting, though absolute differences were modest and driven by HER2 IHC 1+ BC. ERBB2 CNV merits further investigation in HER2-negative BC.

Evolution of low HER2 expression between early and advanced-stage breast cancer

BACKGROUND

Low human epidermal growth factor receptor 2 (HER2) expression is emerging as an actionable biomarker for the treatment of breast cancer (BC) with novel anti-HER2 drugs. However, the evolution of this biomarker during the course of disease is still poorly characterised, and controversial data exist on its prognostic implications.

METHODS

We reviewed data of patients with HER2-negative BC according to the latest ASCO/CAP guidelines referred between January 2014 and December 2020. We grouped patients based on the immunohistochemistry (IHC) expression of HER2, HER2-zero (IHC 0) and HER2-low subgroup (IHC 1+ or 2+/ISH-negative) and evaluated the evolution of HER2 expression between the primary tumour and the first biopsy collected in the advanced setting. Disease-free survival, overall survival and progression-free survival were compared between patients with HER2-zero and HER2-low expression on the primary tumour.

RESULTS

232 patients were included in the analysis. Among the overall population, there was a relevant discordance in HER2 expression between the primary tumour and the matched biopsy (K = 0.33, 95%CI 0.21-0.44): 44% of the HER2-zero primary tumour showed an increased HER2 score on biopsy, and 22% of the HER2-low primary tumours turned into HER2-IHC 0. The findings in the sub-populations of hormone-receptors positive (K = 0.32, 95%CI 0.19-0.45) and triple-negative tumours (K = 0.18, 95%CI -0.09-0.46) were consistent with the primary analysis. No difference in survival outcomes was observed between HER2-low and HER2-zero primary tumours.

CONCLUSIONS

HER2-low expression is dynamic in BC and may be enriched in the advanced-stage setting. No prognostic significance was demonstrated for HER2-low expression.

Landscape of HER2-low metastatic breast cancer (MBC): results from the Austrian AGMT_MBC-Registry

Background

About 50% of all primary breast cancers show a low-level expression of HER2 (HER2-low), defined as immunohistochemically 1+ or 2+ and lack of HER2 gene amplification measured by in situ hybridization. This low HER2 expression is a promising new target for antibody–drug conjugates (ADCs) currently under investigation. Until now, little is known about the frequency and the prognostic value of low HER2-expression in metastatic breast cancer (MBC).

Patients and methods

The MBC-Registry of the Austrian Study Group of Medical Tumor Therapy (AGMT) is a multicenter nationwide ongoing registry for MBC patients in Austria. Unadjusted, univariate survival probabilities of progression-free survival (PFS) and overall survival (OS) were calculated by the Kaplan–Meier method and compared by the log-rank test. Multivariable adjusted hazard ratios were estimated by Cox regression models. In this analysis, only patients with known HER2 status and available survival data were included.

Results

As of 11/15/2020, 1,973 patients were included in the AGMT-MBC-Registry. Out of 1,729 evaluable patients, 351 (20.3%) were HER2-positive, 608 (35.2%) were HER2-low and 770 (44.5%) were completely HER2-negative (HER2-0). Low HER2-expression was markedly more frequent in the hormone-receptor(HR)+ subgroup compared to the triple-negative subgroup (40% vs. 23%). In multivariable analysis, low HER2 expression did not significantly influence OS neither in the HR+ (HR 0.89; 95% CI 0.74–1.05; P = 0.171) nor in the triple-negative subgroup (HR 0.92; 95% CI 0.68–1.25; P = 0.585), when compared to completely HER2-negative disease. Similar results were observed when HER2 IHC 2+ patients were compared to IHC 1+ or 0 patients.

Conclusion

Low-HER2 expression did not have any impact on prognosis of metastatic breast cancer in this real-world population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01492-x.