Moving HER2-low breast cancer predictive and prognostic data from clinical trials into the real world

Comparison of the Pathological Complete Response Rate and Survival Between HER2-Low and HER2-Zero Breast Cancer in Neoadjuvant Chemotherapy Setting: A Systematic Review and Meta-Analysis

Although HER2-low breast cancer (BC) constitutes almost 50% of all BC types, its impact on the pathological complete response (pCR) rate and survival in early BC is uncertain. As a result, a systematic review was conducted to compare the pCR rate and survival of HER2-low and HER2-zero BC in the neoadjuvant chemotherapy (NACT) setting. Two reviewers independently performed literature searches using EMBASE, PubMed, and Cochrane Libraries internet databases up to June 2023. Finally, 29 studies with 178,294 patients were included. HER2-low BC had a considerably lower pCR rate compared to HER2-zero BC in the entire population (Risk Ratio [RR] = 0.68, P < .001) and in the hormone receptor (HR)-positive subgroup (RR = 0.73, P = .009), but not in the HR-negative subgroup (RR = 0.99, P = .755). Furthermore, patients with HER2-low BC exhibited prolonged disease-free survival (DFS) and overall survival (OS) compared to those with HER2-zero BC, observed in both the entire cohort (DFS: P = .004; OS: P = .008) and the HR-negative subgroup (DFS: P = .009; OS: P < .001). In the HR-positive population, OS was superior in HER2-low BC patients (P < .001), whereas no significant differences in DFS were observed (P = .064). Our findings imply that the pCR rate and prognosis of HER2-low BC are distinguished from those of HER2-zero BC in early BC treated with NACT, which contributes to a better knowledge of the BC subgroup.

Molecular and Clinical Portrait of HER2-low Invasive Lobular Carcinomas

Invasive lobular carcinomas (ILCs) have a low frequency of ERBB2 amplification, therefore restricting the use of conventional anti-HER2 therapies for this histologic special type. Conversely, ILCs with low HER2 overexpression may represent a broader target for the use of emerging antibody drug conjugate therapies targeting HER2, since these treatments have proven effective in HER2-low breast cancers. Very scarce data about HER2-low ILCs have been so far published, although these tumors could have different prevalence and histomolecular specificities compared with invasive breast carcinoma of no special type (IBC-NST). Our aims in that context were to decipher the clinicopathological and molecular features of a large series of HER2-low ILCs. Comparative evaluation of HER2-low prevalence was done based on a retrospective series of 7970 patients from Institut Curie, with either primary invasive lobular (N = 1103) or no special type (N = 6867) invasive carcinoma. Clinicopathological and molecular analyses of HER2-zero, HER2-low, and HER2-positive ILCs were performed on a subgroup of 251 patients who underwent surgery for a primary ILC between 2005 and 2008. The mutational profile of these 251 cases was determined from RNAseq data. Compared with HER2-negative IBC-NSTs, the HER2-negative ILCs were found to display a higher frequency of HER2-zero cases (59.4% vs 53.7%) and a lower frequency of HER2-low (40.6% vs 46.3%) (P < .001). Clinicopathological features associated with HER2-low status (vs HER2-zero) in ILC were older age, postmenopausal status, nonclassic ILC histological types, higher grade, proliferation, and estrogen receptor expression levels. Survival curve analysis showed a significantly lower risk of local recurrence for HER2-low (vs HER2-zero) ILCs, but no association was found between HER2 status and either breast cancer-specific survival or distant metastasis-free interval. ERBB3 was the unique mutated gene exclusively associated with HER2-low ILCs yet being mutated at a low frequency (7.1%) (false discovery rate < 0.05). In conclusion, HER2-low ILCs exhibit their own particularities, both on clinical-pathological and molecular levels. Our findings call for larger multicenter validation studies.

Survival outcomes in HER2-low versus HER2-zero breast cancer after neoadjuvant chemotherapy: a meta-analysis

BACKGROUND

The survival outcomes in HER2-low versus HER2-zero breast cancer (BC) after neoadjuvant chemotherapy (NACT) remain unclear. The meta-analysis was conducted to summarize current evidence about the survival outcomes in HER2-low versus HER2-zero BC.

METHODS

We conducted a systematic search in PubMed and EMBASE databases to identify relevant studies.

RESULTS

A total of 14 studies with 53,714 patients were included. Overall, 34,037 patients (63.37%) were HER2-low, and 19,677 patients (36.63%) were HER2-zero. Patients with HER2-low tumors had a significantly lower pathological complete response (pCR) rate than patients with HER2-zero tumors, regardless of the hormone receptor status. Compared with HER2-zero breast cancer, the overall survival (OS) and disease-free survival (DFS) of HER2-low BC were longer in the overall cohort (HR = 0.72; 95% CI = 0.61-0.85; P < 0.0001; HR = 0.83; 95% CI = 0.75-0.92; P = 0.0002); however, no differences were observed in terms of OS and DFS between HER2-low and HER2-zero BC in the HR-negative group. In the HR-positive group, HER2-low status had no significant impact on OS, while significantly associated with increased DFS (HR = 0.85; 95% CI = 0.76-0.96; P = 0.007).

CONCLUSION

These results suggest that although HER2-low BC has a poor response to NACT, it is correlated with favorable OS and DFS after NACT in the overall cohort as well as longer DFS in the HR-positive group.

Open questions, current challenges, and future perspectives in targeting human epidermal growth factor receptor 2-low breast cancer

Approximately 60% of traditionally defined human epidermal growth factor receptor 2 (HER2)-negative breast cancers express low levels of HER2 [HER2-low; defined as immunohistochemistry (IHC) 1+ or IHC 2+/in situ hybridization (ISH)-]. HER2-low breast cancers encompass a large percentage of both hormone receptor-positive (up to 85%) and triple-negative (up to 63%) breast cancers. The DESTINY-Breast04 trial established that HER2-low tumors are targetable, leading to the approval of trastuzumab deruxtecan (T-DXd) as the first HER2-directed therapy for the treatment of HER2-low breast cancer in the United States and Europe. This change in the clinical landscape results in a number of questions and challenges-including those related to HER2 assessment and patient identification-and highlights the need for careful assessment of HER2 expression to identify patients eligible for T-DXd. This review provides context for understanding how to identify patients with HER2-low breast cancer with respect to sample types, scoring and reporting HER2 status, and testing methods and assays. It also discusses management of important T-DXd-related adverse events. Available evidence supports the efficacy of T-DXd in patients with any history of IHC 1+ or IHC 2+/ISH- scores; however, future research may further refine the population who could benefit from T-DXd or other HER2-directed therapies and identify novel methods for patient identification. Because HER2 expression can change with disease progression or treatment, and variability exists in scoring and interpretation of HER2 status, careful re-evaluation in certain scenarios may help to identify more patients who may benefit from T-DXd.

Factors Affecting Pathological Complete Response in Locally Advanced Breast Cancer Cases Receiving Neoadjuvant Therapy: A Comprehensive Literature Review

Determining pathological complete response (pCR) could be an important step in planning individual treatment, hence improving the prognosis in terms of survival. Achieving breast pCR not only improves survival but is also linked to a disease-free axilla, therefore increasing the likelihood of avoiding axillary surgery safely. The current trend in de-escalating axillary management surgically or in applying radiotherapy to the axilla is dependent primarily on breast cancer (BC) patients achieving pCR. Studies have demonstrated that certain characteristics can predict pCR, even though it is still difficult to identify these elements. A review of the literature was carried out to determine these factors and their clinical applications. A search was carried out in the MEDLINE database using PubMed, Google Scholar, and EMBASE. This yielded 1368 studies, of which 60 satisfied the criteria. The studies were categorized according to the subject they dealt with. These parameters included age, race, subtypes, clinicopathological, immunological, imaging, obesity, Ki-67 status, vitamin D, and genetics. These factors, in combination, can be used for specific subtypes to individualize treatment and monitor response to therapy. The predictors of pCR are diverse and should be utilized to personalize patient treatment, ultimately inducing the best outcomes. These determinants can also be employed for monitoring responses to neoadjuvant therapy, thereby adjusting treatment. The development of standardized markers for the diversity of BC subtypes still needs additional future research. These factors must be applied in concert in order to provide optimal results.

Comprehensive genomic characterization of HER2-low and HER2-0 breast cancer

The molecular underpinnings of HER2-low and HER2-0 (IHC 0) breast tumors remain poorly defined. Using genomic findings from 1039 patients with HER2-negative metastatic breast cancer undergoing next-generation sequencing from 7/2013-12/2020, we compare results between HER2-low (n = 487, 47%) and HER2-0 tumors (n = 552, 53%). A significantly higher number of ERBB2 alleles (median copy count: 2.05) are observed among HER2-low tumors compared to HER2-0 (median copy count: 1.79; P = 2.36e-6), with HER2-0 tumors harboring a higher rate of ERBB2 hemideletions (31.1% vs. 14.5%). No other genomic alteration reaches significance after accounting for multiple hypothesis testing, and no significant differences in tumor mutational burden are observed between HER2-low and HER2-0 tumors (median: 7.26 mutations/megabase vs. 7.60 mutations/megabase, p = 0.24). Here, we show that the genomic landscape of HER2-low and HER2-0 tumors does not differ significantly, apart from a higher ERBB2 copy count among HER2-low tumors, and a higher rate of ERBB2 hemideletions in HER2-0 tumors.

Can we define breast cancer HER2 status by liquid biopsy?

Human Epidermal growth factor Receptor 2 (HER2) assessment is crucial for breast cancer treatment. Therapeutic decisions for recurrent cases often rely on primary tumor status. However, mounting evidence suggests that tumors show dynamic changes and up to 10% of breast cancer modify their initial status during progression. It is still debated whether these changes reflect a biological evolution of the disease or are secondary to primary tumor heterogeneity. Certainly, repeating HER2 assessment during breast cancer trajectory is important for the increasing availability of effective anti-HER2 drugs. In response to this need, circulating biomarkers such as circulating tumor cells (CTCs) and cell-free circulating tumor DNA (ctDNA) offer the potential to safely and repeatedly assess HER2 status over time. This chapter outlines current methods for testing HER2 in CTCs and ctDNA, and reviews clinical trials evaluating its prognostic and predictive value in patients with breast cancer, as well as recent advances in the field.

ESMO expert consensus statements (ECS) on the definition, diagnosis, and management of HER2-low breast cancer

Human epidermal growth factor receptor 2 (HER2)-low breast cancer has recently emerged as a targetable subset of breast tumors, based on the evidence from clinical trials of novel anti-HER2 antibody-drug conjugates. This evolution has raised several biological and clinical questions, warranting the establishment of consensus to optimally treat patients with HER2-low breast tumors. Between 2022 and 2023, the European Society for Medical Oncology (ESMO) held a virtual consensus-building process focused on HER2-low breast cancer. The consensus included a multidisciplinary panel of 32 leading experts in the management of breast cancer from nine different countries. The aim of the consensus was to develop statements on topics that are not covered in detail in the current ESMO Clinical Practice Guideline. The main topics identified for discussion were (i) biology of HER2-low breast cancer; (ii) pathologic diagnosis of HER2-low breast cancer; (iii) clinical management of HER2-low metastatic breast cancer; and (iv) clinical trial design for HER2-low breast cancer. The expert panel was divided into four working groups to address questions relating to one of the four topics outlined above. A review of the relevant scientific literature was conducted in advance. Consensus statements were developed by the working groups and then presented to the entire panel for further discussion and amendment before voting. This article presents the developed statements, including findings from the expert panel discussions, expert opinion, and a summary of evidence supporting each statement.

Prognostic value of HER2-low status in breast cancer: a systematic review and meta-analysis

BACKGROUND

Human epidermal growth factor receptor 2 (HER2)-low expression in breast cancer has been recently identified as a new therapeutic target. However, it is unclear if HER2-low status has an independent impact on prognosis.

MATERIALS AND METHODS

A systematic literature research was carried out to identify studies comparing survival outcomes of patients affected by HER2-low versus HER2-zero breast cancer. Using random-effects models, pooled hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for progression-free survival (PFS) and overall survival (OS) in the metastatic setting as well as disease-free survival (DFS), OS and pathological complete response (pCR) in the early setting. Subgroup analyses by hormone receptor (HoR) status were carried out. The study protocol is registered on PROSPERO (n.CRD42023390777).

RESULTS

Among 1916 identified records, 42 studies including 1 797 175 patients were eligible. In the early setting, HER2-low status was associated with significant improved DFS (HR 0.86, 95% CI 0.79-0.92, P < 0.001) and OS (HR 0.90, 95% CI 0.85-0.95, P < 0.001) when compared to HER2-zero status. Improved OS was observed for both HoR-positive and HoR-negative HER2-low populations, while DFS improvement was observed only in the HoR-positive subgroup. HER2-low status was significantly associated with a lower rate of pCR as compared to HER2-zero status both in the overall population (OR 0.74, 95% CI 0.62-0.88, P = 0.001) and in the HoR-positive subgroup (OR 0.77, 95% CI 0.65-0.90, P = 0.001). In the metastatic setting, patients with HER2-low breast cancers showed better OS when compared with those with HER2-zero tumours in the overall population (HR 0.94, 95% CI 0.89-0.98, P = 0.008), regardless of HoR status. No significant PFS differences were found.

CONCLUSIONS

Compared with HER2-zero status, HER2-low status appears to be associated with a slightly increased OS both in the advanced and early settings, regardless of HoR expression. In the early setting, HER2-low tumours seem to be associated to lower pCR rates, especially if HoR-positive.

Incidence, Clinicopathologic Features, HER2 Fluorescence In Situ Hybridization Profile, and Oncotype DX Results of Human Epidermal Growth Factor Receptor 2-Low Breast Cancers: Experience From a Single Academic Center

Human epidermal growth factor receptor 2 (HER2)-low breast cancer, defined by an immunohistochemical (IHC) score of 1+ or 2+ with negative in situ hybridization, is emerging as a predictive marker for the use of the antibody-drug conjugate. To understand how this category differs from HER2-zero cases, we investigated clinicopathological characteristics and HER2 fluorescence in situ hybridization results in a large cohort of 1309 continuous HER2-negative invasive breast carcinomas from 2018 to 2021 evaluated by the Food and Drug Administration-approved HER2 IHC test. Additionally, we compared Oncotype DX recurrence scores and HER2 mRNA expression between HER-low and HER2-zero cases in a separate cohort of 438 estrogen receptor-positive (ER+) early-stage breast carcinoma cases from 2014 to 2016. Based on the cohort from 2018 to 2021, the incidence of HER2-low breast cancers was approximately 54%. HER2-low cases had less frequent grade 3 morphology, less frequent triple-negative results, ER and progesterone receptor negativity, and a higher mean HER2 copy number and HER2/CEP17 ratio than HER2-zero cases (P < .0001). Among ER+ cases, HER2-low cases showed significantly less frequent Nottingham grade 3 tumors. In the cohort from 2014 to 2016, HER2-low cases showed significantly higher ER+ percentages, fewer progesterone receptor-negative cases, lower Oncotype DX recurrence scores, and higher HER2 mRNA expression scores than HER2-zero cases. In summary, this is the first study, to our knowledge, using a large cohort of continuous cases evaluated by the Food and Drug Administration-approved HER2 IHC companion diagnostic test for HER2-low expression and HER2 fluorescence in situ hybridization profile in a real-world setting. Although HER2-low cases showed a higher HER2 copy number, ratio, and mRNA level than HER2-zero cases statistically, such small differences are unlikely to be biologically or clinically meaningful. However, our study suggests that HER2-low/ER+ early-stage breast carcinoma may represent a less aggressive group of breast carcinoma, given its association with a lower Nottingham grade and Oncotype DX recurrence score.

The Effect of HER2-Low Status on Pathological Complete Response and Survival in Triple-Negative Breast Cancer: A Systemic Review and Meta-Analysis

This meta-analysis conducted a comprehensive analysis of research investigating the correlation between HER2 expression levels and treatment outcomes in early-stage triple-negative breast cancer (TNBC) patients. We systematically searched major databases for studies published up to January 01, 2023. The data from various studies examined the relationship between HER2-zero and HER2-low tumors in terms of pathological complete response (pCR) rates, disease-free survival (DFS), and overall survival (OS) outcomes. The odds ratio (OR) and 95% confidence interval (CI) by the number of events were calculated using the Mantel-Haenszel method to analyze pCR. The hazard ratio and 95% CI were calculated using the inverse variance method for DFS and OS. In all comparisons, I² was 0% and no heterogeneity was detected. A total of 12 retrospective studies involving 4094 patients were included. Thirty-six percent of the patients were in the HER2-low group. All 12 studies were included in the pooled analysis for pCR, and there was no difference between HER2-zero and HER2-low (40% vs. 38%, respectively; pooled OR:1.01 95% CI 0.88-1.16; I²: 0%). Four studies were included in the pooled analysis for DFS and 3 in the OS analysis. DFS and OS were significantly better in the HER2-low group (pooled hazard ratio: 0.67 for DFS, 0.64 for OS). There was no difference between HER2-low and HER2-zero in terms of pCR in early-stage TNBC. However, HER2-low was found to be associated with prolonged DFS and OS. PROSPERO REGISTRATION NUMBER: CRD42023391002.

Low HER2 expression is a predictor of poor prognosis in stage I triple-negative breast cancer

Introduction

Triple-negative breast cancer (TNBC) is negative for hormone receptors and human epidermal growth factor receptor 2 (HER2). In stage I TNBC, adjuvant therapy or follow-up are performed according to risk factors, but clinical trial data is scarce. In recent years, it has been reported that HER2-low cases (1+/2+ and in situ hybridization negative) have different prognoses than HER2-0 cases. However, the risk of recurrence and risk factors in this HER2-low population for stage I TNBC have not yet been investigated.

Methods

Herein, out of 174 patients with TNBC who underwent surgery from June 2004 to December 2009 at the National Cancer Center Hospital (Tokyo), we retrospectively examined 42 cases diagnosed as T1N0M0 TNBC after excluding those treated with preoperative chemotherapy.

Results

All patients were female, the median age was 60.5 years, and 11 cases were HER2-low and 31 cases were HER2-0. The median follow-up period was 121 months. Postoperative adjuvant therapy was administered in 30 patients and recurrence occurred in 8 patients. HER2-low cases showed a significantly shorter disease-free survival (HR: 7.0; 95% CI: 1.2– 40.2; P=0.0016) and a trend towards shorter overall survival (hazard ratio [HR]: 4.2, 95% confidence interval [CI]: 0.58–31.4) compared with that of HER2-0 cases. HER2 was also identified as a factor for poor prognosis from the point- estimated values in univariate and multivariate analyses after confirming that there was no correlation between the other factors.

Conclusion

For patients with stage I TNBC, the HER2-low population had a significantly worse prognosis than the HER2-0 population.

Comparison of HER2-zero and HER2-low in terms of clinicopathological factors and survival in early-stage breast cancer: A systematic review and meta-analysis

BACKGROUND

The prognostic differences between HER2-zero and HER2-low breast cancer (BC) remain unclear. Purpose of this meta-analysis is to investigate the differences between HER2-low and HER2-zero in terms of clinicopathological factors and survival outcomes in early-stage BC.

METHODS

We searched major databases and congress proceedings until November 1, 2022 to identify studies comparing HER2-zero and HER2-low in early-stage BC. HER2-zero immunohistochemically (IHC) was defined as score 0, while HER2-low was defined as IHC 1+ or 2+/in situ hybridization negative.

RESULT

A total of 23 retrospective studies involving 636,535 patients were included. HER2-low rate was 67.5% in the hormone receptor (HR)-positive group, while this rate was 48.6% in the HR-negative group. In the analysis of clinicopathological factors by HR status, the proportion of premenopausal patients within the HR-positive group was greater in the HER2-zero arm (66.5% vs 61.8%), whereas grade 3 tumors (74.2% vs 71.5%), patients younger than 50 years of age (47.3% vs 39.6%), and T3-T4 tumors (7.7% vs 6.3%) within the HR-negative group was higher in the HER2-zero arm. In both the HR-positive and HR-negative groups, the HER2-low arm showed significantly improved results for disease-free survival (DFS) and overall survival (OS). The hazard ratios for DFS and OS in the HR-positive group were 0.88 (95% CI 0.83-0.94) and 0.87 (95% CI 0.78-0.96), respectively. In the HR-negative group, the hazard ratios for DFS and OS were 0.87 (95% CI 0.79-0.97) and 0.86 (95% CI 0.84-0.89), respectively.

CONCLUSION

In early-stage BC, HER2-low is associated with better DFS and OS compared to HER2-zero, regardless of HR status.

Pathological complete response and prognosis after neoadjuvant chemotherapy in patients with HER2-low breast cancer

BACKGROUND

The development of novel human epidermal growth factor receptor 2 (HER2) antibody drug conjugates brings encouraging opportunities for the treatment of HER2-low breast cancer. In this study, we investigated the clinical factors and prognosis of HER2-low breast cancer after neoadjuvant chemotherapy (NAC).

METHODS

Data from patients diagnosed with HER2-zero or HER2-low breast cancer at a single center between January 2017 and December 2021 who underwent NAC followed by surgery were retrospectively reviewed. HER2 status was detected by immunohistochemistry (IHC) and fluorescence in-situ hybridization (FISH), and classified as HER2-zero (IHC 0), HER2-low (IHC 1+ or IHC 2+ and FISH-), and HER2-positive (IHC 3+ or IHC 2+ and FISH+). Baseline characteristics were analyzed and compared between the HER2-low and HER2-zero groups. Survival outcomes were analyzed using the Kaplan-Meier method with the log-rank test and Cox proportional-hazards regression analysis.

RESULTS

The sample comprised 132 patients with HER2-zero [n = 62 (47.0 %)] and HER2-low [n = 70 (53.0 %)] breast cancer. Relative to the HER2-zero group, the HER2-low group contained larger proportions of patients with hormone receptor (HR) positivity (37.1 % vs. 75.7 %, P < 0.001) and low nuclear grades and Ki-67 indices (both P < 0.05). The pathological complete response (pCR) rate was significantly lower in the HER2-low group than in the HER2-zero group (20.0 % vs. 37.1 %, P = 0.03). At the final follow-up [median 20 (range 4-66) months], patients with HER2-low status had significantly favorable disease-free survival (DFS) and overall survival (OS) outcomes relative to those with HER2-zero status (87.1 % vs. 71.0 %, P = 0.02 and 94.3 % vs. 82.3 %, P = 0.02, respectively). HER2-low status and pCR were independent prognostic factors for DFS [hazard ratio (HR) = 0.31, 95 % confidence interval (CI) 0.13-0.75, P = 0.009 and HR = 0.08, 95 % CI 0.01-0.67, P = 0.02, respectively].

CONCLUSION

This analysis revealed that HER2-low status is associated significantly with HR positivity and low nuclear grades, Ki-67 indices, and pCR rate. It is also associated with favorable DFS and OS outcomes after NAC. HER2-low status and pCR are independent prognostic factors for DFS.

Current Biological, Pathological and Clinical Landscape of HER2-Low Breast Cancer

HER2-low breast cancer (BC) is a newly defined subset of HER2-negative BC that has HER2 immunohistochemical (IHC) score of 1+ or score of 2+/in situ hybridization (ISH) negative phenotype. Recent clinical trials have demonstrated significant clinical benefits of novel HER2 directing antibody-drug conjugates (ADCs) in treating this group of tumors. Trastuzumab-deruxtecan (T-Dxd), a HER2-directing ADC was recently approved by the U.S. Food and Drug Administration as the first targeted therapy to treat HER2-low BC. However, HER2-low BC is still not well characterized clinically and pathologically. This review aims to update the current biological, pathological and clinical landscape of HER2-low BC based on the English literature published in the past two years and to propose the future directions on clinical management, pathology practice, and translational research in this subset of BC. We hope it would help better understand the tumor biology of HER2-low BC and the current efforts for identifying and treating this newly recognized targetable group of BC.