HER2-Low Status Is Not Accurate in Breast Cancer Core Needle Biopsy Samples: An Analysis of 5610 Consecutive Patients

Prevalence and concordance of HER2-low and HER2-ultralow status between historical and rescored results in a multicentre study of breast cancer patients in China

BACKGROUND

Accurately assessing HER2-low (immunohistochemistry [IHC] 1 + and IHC 2+/in situ hybridization [ISH]-) and HER2-ultralow (IHC > 0 < 1+) is essential given the emergence of novel therapies. Thorough understanding of the reproducibility of rescoring IHC stained slides or re-staining archived tissue slides is essential.

METHODS

2,869 breast cancer patients diagnosed between July 2021 and July 2022 from 10 hospitals in China were included in this multicentre study. The prevalence of different HER2 expression levels and distribution of HER2 IHC scores were assessed by HER2 status determination from rescored historical slides. Concordance was evaluated across historical results versus rescored results, historical results versus re-stained results, and leading center results versus local site results. Clinicopathological characteristics were retrospectively analyzed as well.

RESULTS

HER2 IHC 0, IHC 1+, IHC 2+, and IHC 3 + were identified in 682 (23.8%), 871 (30.4%), 801 (27.9%), and 515 (18.0%) cases, respectively. HER2-positive, HER2-low, and HER2 IHC 0 (HER2-ultralow and IHC null) were identified in 21.7%, 54.5%, and 23.8% of cases, respectively. The prevalence of HER2-ultralow and IHC null was 10.6% and 13.2%, respectively. The concordance for HER2-ultralow was 43.3%; 30% of cases that were scored as HER2-ultralow at local sites were rescored as HER2-null and 26.7% of cases were rescored as IHC 1 + at the leading site. Overall, there was substantial agreement (83.1%) between rescored and historical IHC results. A high concordance rate of 91.7% was observed for HER2-low classification.

CONCLUSIONS

This is the first multicenter study to determine the prevalence of HER2-low and HER2-ultralow based on rescored results in the Chinese breast cancer population. The concordance analysis carries important implications for the diagnosis of HER2-low and HER2-ultralow cases in clinical practice. The relatively low concordance in identifying HER2-ultralow suggested that the reproducibility of scoring HER2-ultralow needed to be improved through training.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT05203458.

Comprehensive analysis of HER2 Low Breast Cancer Response to Neoadjuvant Chemotherapy, a Retrospective Cohort Study

BACKGROUND

This study aimed to identify the response and survival outcomes of HER2-low patients following neoadjuvant chemotherapy (NAC).

METHOD

A retrospective cohort of patients who received NAC in the Department of Breast Surgery at Peking Union Medical College Hospital (PUMCH) from September 27, 2016, to January 23, 2024, was reviewed. Multivariate logistic regression and Cox proportional hazards models were used to identify factors associated with pathological complete response (pCR) and survival outcomes. The Kaplan-Meier method was applied to compare survival outcomes between HER2-zero and HER2-low patients.

RESULT

Four hundred and twenty-one patients meeting the inclusion criteria. The pCR rate of HER2-zero patients was significantly higher than that of HER2-low patients after adjusting for confounders (OR = 2.83, 95% CI: 1.44-5.65, adjusted P = .003). HER2-low patients demonstrated the most stable status after NAC within the hormone receptor (HR)-positive subset (80.82%) and the most unstable status within the HR-negative subset (57.69%). HER2-zero status was associated with worse disease-free survival (DFS) (HR = 1.94, 95% CI: 1.13-3.32, adjusted P = .02), but not with overall survival (OS) (HR = 1.18, 95% CI: 0.59-2.37, P = .65). HER2-zero patients had significantly worse DFS than HER2-low patients in the entire cohort (P = .014) and the HR-positive subset (P < .001). pCR could serve as a surrogate endpoint of favorable survival outcomes for HER2-zero patients, but not for HER2-low patients.

CONCLUSION

HER2-low patients might exhibit distinct characteristics compared with HER2-zero patients following NAC. Further multicenter, prospective studies are warranted to validate the conclusions of this exploratory research and assess whether HER2-low expression could serve as a new clinical subtype for evaluating NAC treatment outcomes.

HER2-low status as a distinct breast cancer subtype: myth or truth? Analysis of the WSG trials WSG-ADAPT-HR+/HER2-, WSG-PlanB, and WSG-ADAPT-TN

BACKGROUND

New data show that not only HER2-overexpressing breast cancer (BC) tumors but also HER2-low tumors, classically considered as HER2-negative, respond to HER2-targeting antibody-drug-conjugates. Our objective was to analyze the prevalence of HER2-low BC in a pooled analysis of contemporary early BC trials and to evaluate its role as a prognostic factor in terms of survival in comparison to HER2-zero BC.

METHODS

We evaluated 5598 patients with locally HR + /HER2- BC from the screening cohort of WSG-ADAPT-HR + /HER2-, 2592 patients with HR + /HER2- or HR-/HER2- from the adjuvant WSG-PlanB trial, and 336 patients from the WSG-ADAPT-TN trial. Central HER2 testing was performed prospectively in WSG-ADAPT and retrospectively in WSG-PlanB. Following ASCO/CAP guidelines, HER2-low status was defined as immunohistochemistry (IHC) 1 + or 2 + and in situ hybridization (ISH)-negative, and HER2-zero was defined as IHC 0. Agreement between HER2 assessments was evaluated with Cohen's kappa coefficient, and effects of HER2 status on pathological complete response (pCR) and on survival were analyzed with logistic regression and Cox proportional hazards models, respectively.

FINDINGS

In WSG-ADAPT-HR + /HER2-, 3198 (64.6%) tumors were HER2-low by the central and 3096 (55.6%) by the local histology (agreement for HER2-low status was 61.0%). In HR + /HER2- cases from WSG-PlanB, 601 tumors (28.7%) were HER2-low. In both cohorts, HER2-low status was significantly associated with higher ERBB2 mRNA expression by Oncotype DX test in comparison to HER2-zero: mean 9.3 vs. 9.1 (p < .001) by local HER2 assessment in WSG-ADAPT and mean 9.2 vs. 8.8 (p < .001) in WSG-PlanB. Furthermore, patients with HER2-low tumors in WSG-ADAPT-HR + /HER2- significantly less often had a pCR compared to the HER2-zero tumors (p = .015). No significant difference was observed in (invasive and/or distant) disease-free survival (DFS) between centrally HER2-low and HER2-zero tumors in both HR + /HER2- cohorts (WSG-ADAPT-HR + /HER2- distant DFS: unadjusted HR = 1.06, 95%CI 0.83-1.36, similar results for local assessment; WSG-PlanB DFS: unadjusted HR = 1.28, 95%CI 0.91-1.82). In the HR-/HER2- WSG-PlanB cohort, centrally HER2-low tumors (10.5%) were associated with better DFS (unadjusted HR = 0.21, 95%CI 0.05-0.83), this association was not observed in the WSG-ADAPT-TN.

CONCLUSION

The prevalence of HER2-low status varied between the analyzed trials. Our results show that survival does not differ between HER2-low and HER2-zero tumors in HR + /HER2- cohorts; however, HER2-low status appears to have an inconsistent impact on survival in TNBC. Therefore, our findings do not support the characterization of HER2-low status as a distinct BC subtype.

Multiparametric MRI Radiomics With Machine Learning for Differentiating HER2-Zero, -Low, and -Positive Breast Cancer: Model Development, Testing, and Interpretability Analysis

BACKGROUND. MRI radiomics has been explored for three-tiered classification of HER2 expression levels (i.e., HER2-zero, HER2-low, or HER2-positive) in patients with breast cancer, although an understanding of how such models reach their predictions is lacking. OBJECTIVE. The purpose of this study was to develop and test multiparametric MRI radiomics machine learning models for differentiating three-tiered HER2 expression levels in patients with breast cancer, as well as to explain the contributions of model features through local and global interpretations with the use of Shapley additive explanation (SHAP) analysis. METHODS. This retrospective study included 737 patients (mean age, 54.1 ± 10.6 [SD] years) with breast cancer from two centers (center 1 [n = 578] and center 2 [n = 159]), all of whom underwent multiparametric breast MRI and had HER2 expression determined after excisional biopsy. Analysis entailed two tasks: differentiating HER2-negative (i.e., HER2-zero or HER2-low) tumors from HER2-positive tumors (task 1) and differentiating HER2-zero tumors from HER2-low tumors (task 2). For each task, patients from center 1 were randomly assigned in a 7:3 ratio to a training set (task 1: n = 405; task 2: n = 284) or an internal test set (task 1: n = 173; task 2: n = 122); patients from center 2 formed an external test set (task 1: n = 159; task 2: n = 105). Radiomic features were extracted from early phase dynamic contrast-enhanced (DCE) imaging, T2-weighted imaging, and DWI. For each task, a support vector machine (SVM) was used for feature selection, a multiparametric radiomics score (radscore) was computed using feature weights from SVM correlation coefficients, conventional MRI and combined models were constructed, and model performances were evaluated. SHAP analysis was used to provide local and global interpretations of the model outputs. RESULTS. In the external test set, for task 1, AUCs for the conventional MRI model, radscore, and the combined model were 0.624, 0.757, and 0.762, respectively; for task 2, the AUC for radscore was 0.754, and no conventional MRI model or combined model could be constructed. SHAP analysis identified early phase DCE imaging features as having the strongest influence for both tasks; T2-weighted imaging features also had a prominent role for task 2. CONCLUSION. The findings indicate suboptimal performance of MRI radiomics models for noninvasive characterization of HER2 expression. CLINICAL IMPACT. The study provides an example of the use of SHAP interpretation analysis to better understand predictions of imaging-based machine learning models.

HER2-low status improves prognosis prediction in breast cancer patients receiving neoadjuvant treatment: A comparison of pathological stage, modified CPS+EG scoring system, and Neo-Bioscore

Objective

To explore the prognosis-predictive influence of human epidermal growth factor receptor 2 (HER2)-low status in breast cancer patients after neoadjuvant therapy (NAT).

Methods

Consecutive patients with invasive breast cancer who underwent NAT and surgery from January 2009 to December 2020 at multiple centers were included. A modified CPS+EG scoring system that integrates HER2-low status, CPS+EGHlow was developed. Multiple scoring systems were compared via receiver operating characteristic curves with the area under curve (AUC), the Akaike information criterion, the C-index, and calibration curves.

Results

A total of 2,141 patients were included: 1,074, 640, and 427 patients in the training, internal validation, and external validation groups, respectively. HER2-low patients had a significantly better breast cancer-specific survival (BCSS, P=0.008) and recurrence-free interval (RFI, P=0.030) compared to HER2-zero patients (P=0.038) but inferior outcomes than HER2-amplified ones (BCSS, P=0.002; RFI, P<0.001). The CPS+EGHlow (AUC: 0.846, 0.817, 0.901) could stratify patients according to BCSS in training, internal validation, and external validation group, respectively, overperforming pathological stage (PS) (AUC: 0.746, 0.779, 0.754), CPS+EG (AUC: 0.771, 0.752, 0.748), and Neo-Bioscore (AUC: 0.783, 0.777, 0.786, all P<0.05).

Conclusions

HER2-low status showed a significant prognostic value in breast cancer patients after NAT. The CPS+EGHlow model significantly outperformed PS, CPS+EG, and Neo-Bioscore in clinical outcome prediction, which may guide further therapy targeting HER2-low.

Association between homologous recombination deficiency status and carboplatin treatment response in early triple-negative breast cancer

BACKGROUND

The aim of this study was to assess homologous recombination deficiency (HRD) status and its correlation with carboplatin treatment response in early triple-negative breast cancer (TNBC) patients.

METHODS

Tumor tissues from 225 consecutive TNBC patients were evaluated with an HRD panel and homologous recombination-related (HRR) gene expression data. HRD positivity was defined as a high HRD score and/or BRCA1/2 pathogenic or likely pathogenic mutation. Clinicopathological factors, neoadjuvant treatment response, and prognosis were analyzed with respect to HRD status in these TNBC patients.

RESULTS

HRD positivity was found in 53.3% of patients and was significantly related to high Ki67 levels (P = 0.001). In patients who received neoadjuvant chemotherapy, HRD positivity (P = 0.005) or a high HRD score (P = 0.003) was significantly associated with a greater pathological complete response (pCR) rate, especially in those treated with carboplatin-containing neoadjuvant regimens (HRD positivity vs. negativity: 50.00% vs. 17.65%, P = 0.040). HRD positivity was associated with favorable distant metastasis-free survival (hazard ratio HR 0.49, 95% confidence interval CI 0.26-0.90, P = 0.022) and overall survival (HR 0.45, 95% CI 0.20-0.99, P = 0.049), irrespective of carboplatin treatment.

CONCLUSION

TNBC patients with high HRDs had high Ki67 levels and BRCA mutations. HRD-positive TNBC patients treated with carboplatin had a higher pCR rate. Patients with HRD positivity had a better prognosis, irrespective of carboplatin treatment, warranting further evaluation.

Comparison of clinicopathological characteristics, efficacy of neoadjuvant therapy, and prognosis in HER2-low and HER2-ultralow breast cancer

BACKGROUND

This study aims to analyze potential differences in clinicopathology, efficacy of neoadjuvant therapy (NAT), and clinical outcome among HER2-null, HER2-ultralow and HER2-low breast cancers.

METHODS

Consecutive cases of HER2-negative breast cancer that received NAT were included. They were classified as HER2-null (no staining), HER2-ultralow (incomplete faint staining in ≤ 10% of tumour cells) and HER2-low (HER2-1 + or HER2-2+, in situ hybridisation negative). Subgroup analysis was performed based on the HER2 expression level.

RESULTS

Out of 302 patients, 215 (71.19%) were HER2-low, 59 (19.54%) were HER2-ultralow, and 28 (9.27%) were HER2-null. In comparison to the HER2-ultralow group, the HER2-low group exhibited higher expression frequencies of ER (p < 0.001), PR (p < 0.001), and AR (p = 0.004), along with a greater prevalence of the luminal subtype (p < 0.001). The HER2-ultralow group also demonstrated a higher prevalence of lymph node metastasis compared to the HER2-null group (p = 0.026). Varied rates of pathologic complete response (pCR) were observed among the three subgroups: HER2-null, HER2-ultralow, and HER2-low, with rates of 35.71%, 22.03%, and 12.56%, respectively. Only the HER2-low subgroup exhibited a significant difference compared to HER2-null (p = 0.001). Despite variations in pCR rates, the three subgroups exhibited comparable disease-free survival (DFS) (p = 0.571). Importantly, we found HER2-low patients with better treatment response (RCB-0/I) exhibited significantly better DFS than those with significant residual disease (RCB-II/III) (P = 0.036). The overall rate of HER2 immunohistochemical score discordance was 45.24%, mostly driven by the conversion between HER2-0 and HER2-low phenotype. Notably, 32.19% of cases initially classified as HER2-0 phenotype on baseline biopsy were later reclassified as HER2-low after neoadjuvant therapy, and it is noteworthy that 22 out of these cases (78.57%) originally had an HER2-ultralow status in the pretreatment biopsy sample.

CONCLUSIONS

Our results demonstrate the distinct clinicopathological features of HER2-low and HER2-ultralow breast tumors and confirm that RCB is an effective predictor of prognosis in HER2-low populations for the first time. Notably, our findings demonstrate high instability in both HER2-low and HER2-ultralow expression from the primary baseline biopsy to residual disease after NAT. Furthermore, this study is the first to investigate the clinicopathological feature and the effectiveness of NAT for HER2-ultralow breast cancer.

Unveiling the mysteries of HER2-low expression in breast cancer: pathological response, prognosis, and expression level alterations

BACKGROUND

The novel anti-HER2 antibody drug conjugates (ADCs) can effectively improve the long-term survival of patients with HER2-low expression breast cancer. However, pathological responses to neoadjuvant therapy (NAT) within HER2-low expression breast cancer, the relationship between pathological response and prognosis and the transformation of HER2 status are all now poorly understood.

METHODS

The patients with HER2-0 and HER2-low expression breast cancer receiving NAT at Harbin Medical University Cancer Hospital between Jan. 2014 and Nov. 2018 were retrospectively explored. HER2 low expression refers to the IHC 1 + or 2 + and FISH negative. The Kappa test was utilized for analyzing the consistency rate of HER2 expression. To evaluate disease-free survival (DFS) and overall survival (OS), this research employed both the Kaplan-Meier analysis and the Cox regression.

RESULTS

In this study, 178 patients with HER2-0 and 344 patients with HER2-low expression breast cancer were included. In comparison with the HER2-0 group, it is shown that patients in the HER2-low group have more possibility to be younger compared to those 50 years old (P < 0.014), have more premenopausal patients (P < 0.001), a higher proportion of hormone receptor (HR) positive patients (P < 0.001), and less proportion of stage III V patients (P < 0.034). When NAT was finished, the pCR rate became 23.6% in the HER2-0 group while 22.1% in the HER2-low group, and there was also a higher pCR rate in HR- patients in comparison with that in HR + patients (P < 0.01). Considering HER2 expression inconsistency, the overall HER2 inconsistency rate was 30.4% (Kappa = 0.431, P < 0.01). Among patients initially diagnosed as HER2-0, 34% (N = 61) were re-diagnosed as HER2-low after NAT. After stratification by HR expression status, HR+/HER2-0 patients transformed to HER2-low after NAT in 37%, and 32% of HR- patients changed from HER2-0 to HER2-low. In this survival analysis, there were both better DFS rates (P = 0.009) and OS rates (P = 0.026) in the HR-/HER2-low patients in comparison with the HR-/HER2-0 patients, while the HER2-0 and HER2-low patients in the HR + group had no significant survival difference. Additionally, for non-pCR patients, there was better DFS (P = 0.029) and OS (P = 0.038) in the HER2-low group in comparison with that of the HER2-0 group, while no significant survival difference exists between pCR patients.

CONCLUSION

After HR stratification, there are unique clinical characteristics and prognostic outcomes in HER2-low expression breast cancer, which indicates the potential to become a specific molecular subtype of breast cancer. The significant instability of HER2-low expression status between primary tumor and residual invasive disease suggests that multiple detections of HER2 status should be emphasized in NAT strategies.

Association of Oncotype-DX HER2 Single Gene Score With HER2 Expression Assessed by Immunohistochemistry in HER2-low Breast Cancer

Background/Aim

"HER2-low" is an emerging subtype of breast cancer, with a documented role in predicting response to treatment with novel antibody-drug conjugates. It is defined based on immunohistochemistry, but increasing evidence is challenging this approach as appropriate for identifying the HER2-low subgroup, due to both interobserver variability and limitations of the method itself.

Patients and Methods

We retrospectively analyzed data from 430 patients from our departmental databases who had been subjected to an Oncotype-DX score and assessed the correlation of the Oncotype-DX HER2 single-gene score with the HER2 expression on immunohistochemistry. The Oncotype-DX Recurrence Score was also evaluated in the HER2-0 versus HER2-low subgroups.

Results

The HER2 single-gene score was found to accurately correlate with the HER2 result on immunohistochemistry, with a statistically significant difference both between HER2-0 and HER2 +1 tumors (p<0.0001), as well as between HER2 +1 and +2 tumors (p<0.0001). There was no statistically significant difference in the recurrence score between the HER2-0 and the HER2-low subgroups.

Conclusion

Oncotype-DX single-gene scores for HER2 are a potential surrogate marker for assessing the precise HER2 status, with better reproducibility and less interobserver variance compared to immunohistochemistry. The use of rt-PCR emerges as an alternative method of assessment of the HER2-low subgroup.

Concordance of HER2 status between core needle biopsy and surgical resection specimens of breast cancer: an analysis focusing on the HER2-low status

BACKGROUND

Human epidermal growth factor receptor 2 (HER2)-low status has recently gained attention because of the potential therapeutic benefits of antibody-drug conjugates (ADCs) in breast cancer patients. We aimed to investigate the concordance of HER2 status between core needle biopsy (CNB) and subsequent surgical resection specimens focusing on the HER2-low status.

METHODS

This retrospective study was conducted in 1,387 patients with invasive breast cancer whose HER2 status was evaluated in both CNB and surgical resection specimens. The discordance rates between CNB and surgical resection specimens and the clinicopathological features associated with HER2 status discordance were analyzed.

RESULTS

The overall concordance rates of HER2 status between CNB and surgical resection specimens were 99.0% (κ = 0.925) for two-group classification (negative vs. positive) and 78.5% (κ = 0.587) for three-group classification (zero vs. low vs. positive). The largest discordance occurred in CNB-HER2-zero cases with 42.8% of them reclassified as HER2-low in surgical resection. HER2 discordance was associated with lower histologic grade, tumor multiplicity, and luminal A subtype. In multivariate analysis, tumor multiplicity and estrogen receptor (ER) positivity were independent predictive factors for HER2-zero to low conversion.

CONCLUSIONS

Incorporation of HER2-low category in HER2 status interpretation reduces the concordance rate between CNB and surgical resection specimens. Tumor multiplicity and ER positivity are predictive factors for conversion from HER2-zero to HER2-low status. Therefore, HER2 status should be re-evaluated in resection specimens when considering ADCs in tumors exhibiting multiplicity and ER positivity.

Do HER2-Low Tumors Have a Distinct Clinicopathologic Phenotype?

BACKGROUND

Breast cancer subtypes, distinguished by hormone receptor (HR) and HER2 status, have different clinicopathologic features. With recognition of the clinical relevance of HER2-low, there is debate as to whether this is a distinct subtype. Our study aimed to determine whether HER2-low breast cancers have specific clinicopathologic features that differ from those of HER2-negative and HER2-positive cancers.

PATIENTS AND METHODS

A total of 11,072 patients undergoing upfront surgery from 1998 to 2010 were identified from a single-institution prospectively maintained database. HER2 status was classified by immunohistochemistry (IHC)/fluorescence in situ hybridization (FISH) as HER2 negative (41.2%), HER2 low (45%; IHC 1+ or 2+ with negative FISH), and HER2 positive (13.7%), and stratified by HR status. Univariate (UVA) and multivariable multinomial logistic regression analysis (MVA) were performed to determine associations among variables and subtypes.

RESULTS

Compared with HER2-negative tumors, HER2 low was associated with lymphovascular invasion [odds ratio (OR) 1.2, 95% confidence interval (CI) 1.06-1.36; p = 0.003], multifocality (OR 1.26, 95% CI 1.12-1.42; p < 0.001), nodal micrometastasis (OR 1.15, 95% CI 1.02-1.31; p = 0.024), and lower rates of ≥ 3 positive nodes (OR 0.77, 95% CI 0.66-0.90, p = 0.001). When stratified by HR expression, in both HR-positive and HR-negative tumors, age and multifocality were associated with HER2 low on UVA. On MVA, no variables were independently associated with both HR-negative and HR-positive/HER2-low tumors compared with HER2-negative tumors. In contrast, HER2-positive tumors, regardless of HR status, were associated with multifocality and an extensive intraductal component.

CONCLUSION

Clinicopathologic features of HER2-low tumors appear to be primarily related to HR status. Our findings do not support the characterization of HER2 low as a separate subtype.

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.

Pathological complete response, category change, and prognostic significance of HER2-low breast cancer receiving neoadjuvant treatment: a multicenter analysis of 2489 cases

BACKGROUND

HER2-low breast cancers (BC) show a good response to novel anti-HER2 antibody-drug conjugates (ADCs) in advanced setting. Nevertheless, little is known about the response, category change, and prognosis of HER2-low BC receiving neoadjuvant treatment (NAT).

METHODS

Consecutive invasive BC patients who underwent ≥ 4 cycles of NAT and surgery from January 2009 to December 2020 were retrospectively reviewed. HER2-low was defined as IHC 1+ or 2+ and FISH negative. Concordance rates of HER2 and other biomarkers were analyzed by Kappa test. Kaplan-Meier analysis and Cox regression were used to assess the recurrence-free interval (RFI) and overall survival (OS).

RESULTS

A total of 2489 patients were included, of whom 1023 (41.1%) had HER2-low tumors. HER2-low patients had a higher ER positivity rate than HER2-0 patients (78.5% vs. 63.6%, P < 0.001), and a similar breast pathological complete response (pCR) rate (20.6% vs. 21.8%, P = 0.617). Among non-pCR cases, 39.5% of HER2-0 tumors changed to HER2-low, and 14.3% of HER2-low tumors changed to HER2-0 after NAT. Low concordance rates of HER2-low status were found in both ER-positive (Kappa = 0.368) and ER-negative (Kappa = 0.444) patients. Primary HER2-low patients had a significantly better RFI than HER2-0 patients (P = 0.014), especially among ER-positive subset (P = 0.016). Moreover, HER2-low category change was associated with RFI in ER-positive subset (adjusted P = 0.043).

CONCLUSIONS

Compared with HER2-0 patients, HER2-low patients had a high proportion of ER-positive tumor and a similar pCR rate, which were related with better prognosis, especially in residual cases after NAT. A remarkable instability of HER2-low status was found between the primary and residual tumor, indicating re-testing HER2 status after NAT in the new era of anti-HER2 ADCs therapy.

Concordance of HER2-low scoring in breast carcinoma among expert pathologists in the United Kingdom and the republic of Ireland -on behalf of the UK national coordinating committee for breast pathology

BACKGROUND

Recent clinical evidence showed that breast cancer with low HER2 expression levels responded to trastuzumab deruxtecan therapy. The HER2-low cancers comprise immunohistochemistry (IHC) score 1+ and 2+ ISH non-amplified tumours, currently classified as HER2 negative. Little data exists on the reproducibility of pathologists reporting of HER2-low cancer.

PATIENT AND METHODS

Sixteen expert pathologists of the UK National Coordinating Committee for Breast Pathology scored 50 digitally scanned HER2 IHC slides. The overall level of agreement, Fleiss multiple-rater kappa statistics and Cohen's Kappa were calculated. Cases with low concordance were re-scored by the same pathologists after a washout period.

RESULTS

Absolute agreement was achieved in 6% of cases, all of which scored 3+. Poor agreement was found in 5/50 (10%) of cases. This was due to heterogeneous HER2 expression, cytoplasmic staining and low expression spanning the 10% cut-off value. Highest concordance (86%) was achieved when scores were clustered as 0 versus others. Improvement in kappa of overall agreement was achieved when scores 1+ and 2+ were combined. Inter-observer agreement was moderate to substantial in the whole cohort but fair to moderate in the HER2-low group. Similarly, consensus-observer agreement was substantial to almost perfect in the whole cohort and moderate to substantial in the HER2-low group.

CONCLUSION

HER2-low breast cancer suffers from lower concordance among expert pathologists. While most cases can reproducibly be classified, a small proportion (10%) remained challenging. Refining the criteria for reporting and consensus scoring will help select appropriate patients for targeted therapy.