The FDA-Approved Breast Cancer HER2 Evaluation Kit (HercepTest; Dako) May Miss Some HER2-Positive Breast Cancers

Low interobserver agreement among subspecialised breast pathologists in evaluating HER2-low breast cancer

AIMS

Metastatic HER2-low breast cancer (HLBC) can be treated by trastuzumab deruxtecan. Assessment of low levels of HER2 protein expression suffers from poor interobserver reproducibility. The aim of the study was to evaluate the interobserver agreement among subspecialised breast pathologists and develop a practical algorithm for assessing HLBC.

METHODS

Six breast pathologists (4 juniors, 2 seniors) evaluated 106 HER2 immunostained slides with 0/1+expression. Two rounds (R1, R2) of ring study were performed before and after training with a modified Ki-67 algorithm, and concordance was assessed.

RESULTS

Agreement with 5% increments increased from substantial to almost perfect (R1: 0.796, R2: 0.804), and remained substantial for three categories (<1% vs 1%-10% vs >10%) (R1: 0.768, R2: 0.764). Seniors and juniors had almost perfect agreement with 5% increments (R1: 0.859 and 0.821, R2: 0.872 and 0.813). For the three categories, agreement remained almost perfect among seniors (R1: 0.837, R2: 0.860) and substantial among juniors (R1: 0.792, R2: 0.768). Binary analysis showed suboptimal agreement, decreasing for both juniors and seniors from substantial (R1: 0.650 and 0.620) to moderate (R2: 0.560 and 0.554) using the 1% cut-off, and increasing from moderate to substantial (R1: 0.478, R2: 0.712) among seniors but remaining moderate (R1: 0.576, R2: 0.465) among juniors using the 10% cut-off. The average scoring time per case was higher (72 vs 92 s).

CONCLUSIONS

Subspecialised breast pathologists have suboptimal agreement for immunohistochemical evaluation of HLBC using the modified Ki-67 methodology. An urgent need remains for a new assay/algorithm to reliably evaluate HLBC.

Atypical Co-amplification with Co-localization of HER2 Gene in Breast Cancer: Combined IHC/FISH Approach as per ASCO/CAP 2018 Guidelines for Targeted Therapy Eligibility

Breast cancer patients with HER2 gene amplification as assessed by FISH are eligible for HER2-targeted therapy. However, in a small subset of patients, unusual FISH pattern of co-localization and co-amplification can pose challenges in interpretation of the HER2 status and hence to assess the HER2 status accurately; our aim was to report their incidence and analyze them based on latest ASCO/CAP 2018 guidelines. We present seven cases with HER2/CEP17 co-amplification and co-localization from a total 4040 cases referred during the year 2017 to 2021 at Mumbai Reference Laboratory, SRL Diagnostics. Core needle biopsy/excision invasive breast carcinoma specimens from metastatic sites were tested for IHC for expressions of ER, PR, and HER2. The ones which came equivocal on HER2 IHC were then evaluated for HER2 amplification by FISH. Co-amplification and co-localization of HER2 and centromeric 17 was observed with a frequency of 0.1% that falls in the range of 0.5-0.1% as reported from other large-scale studies. Our study showed that implementation of a binary inhouse concurrent assessment with IHC as per the ASCO/CAP 2018 helps to reach the most definitive and accurate HER2 status. Our study is an attempt to report such challenging FISH patterns and their work-up for a better understanding on the interpretation. Cumulative data along with follow-up in these cases would bring an insight into exact therapeutic outcome.

Correlation of HER2 Protein Level With mRNA Level Quantified by RNAscope in Breast Cancer

Trastuzumab deruxtecan (T-DXd) has been approved by the US Food and Drug Administration (FDA) to treat patients with metastatic HER2-positive and HER2-low breast cancer, and clinical trials are examining its efficacy against early-stage breast cancer. Current HER2 immunohistochemical (IHC) assays are suboptimal in evaluating HER2-low breast cancers and identifying which patients would benefit from T-DXd. HER2 expression in 526 breast cancer tissue microarray (TMA) cores was measured using the FDA-approved PATHWAY and HercepTest IHC assays, and the corresponding RNA levels were evaluated by RNAscope. HER2 protein levels by regression analysis using a quantitative immunofluorescence score against cell line arrays with known HER2 protein levels determined by mass spectrometry were available in 48 of the cores. RNAscope was also performed in 32 metastatic biopsies from 23 patients who were subsequently treated with T-DXd, and the results were correlated with response rate. HER2 RNA levels by RNAscope strongly correlated with HER2 protein levels (P < .0001) and with HER2 IHC H-scores from the PATHWAY and HercepTest assays (P < .0001). However, neither protein levels nor RNA levels significantly differed between cases scored 0, ultralow, and 1+ by PATHWAY and HercepTest. The RNA levels were significantly higher (P = .030) in responders (6.4 ± 8.2 dots/cell, n = 12) than those in nonresponders (2.6 ± 2.2, n = 20) to T-DXd. RNAscope is a simple assay that can be objectively quantified and is a promising alternative to current IHC assays in evaluating HER2 expression in breast cancers, especially HER2-low cases, and may identify patients who would benefit from T-DXd.

Quantitative Impact of the 2018 American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) Practice Guideline Update on Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: A Systematic Analysis

CONTEXT.—

The global impact of the new 2018 American Society of Clinical Oncology/College of American Pathologists human epidermal growth factor receptor 2 (HER2) practice guideline update on the overall HER2 status designation, compared with the prior 2013 iteration, is unknown.

OBJECTIVES.—

To report the quantitative impact of the new guideline on HER2 status distribution.

DESIGN.—

The analysis comprised a retrospective cohort of patients from the authors' institution, combined with other peer-reviewed publications that assessed the impact of the 2018 guideline in relation to the 2013 guideline.

RESULTS.—

Our study revealed that the new guideline led to an average 9% reclassification rate for the overall HER2 status, with a net gain in overall HER2 negative designation. This is largely due to reclassification of the equivocal (Group 4) groups. Unexpectedly, infrequent but consistent discordance between Group 1/5 and fluorescence in situ hybridization results are observed across studies (1.8%; 73 of 3965 cases where fluorescence in situ hybridization and immunohistochemistry are both reported).

CONCLUSIONS.—

Early clinical recognition of these resultant changes, including emerging issues of tumor heterogeneity, and potential discordance between immunohistochemistry to fluorescence in situ hybridization, is important for accurate clinical assessment of individual HER2 test results.

HER2 immunohistochemistry staining positivity is strongly predictive of tumor response to neoadjuvant chemotherapy in HER2 positive breast cancer

BACKGROUND

The current recommendation is to reflex test HER2 immunohistochemistry (IHC) equivocal breast cancer cases with fluorescence in situ hybridization (FISH) analysis. Either IHC 3+ or FISH positive cancers are considered HER2 positive (HER2+) and treated with HER2 targeted therapy. This study examined the predictive value of HER IHC or FISH positivity in tumor response to HER2 targeted therapy.

METHODS

Biopsies of 76 HER2+ breast cancer cases were evaluated. All patients were treated with neoadjuvant HER2 targeted therapy and chemotherapy. Tumor response was evaluated on the excisional specimens. Cancers with complete pathologic response (pCR) or MD Anderson residual cancer burden-I (RCB-I) were classified as responders and cancers with RCB-II/III as non-responders. Clinicopathologic parameters were correlated with response.

RESULTS

In univariate analysis, small tumor size, low nuclear grade, high Ki67, HER2 IHC 3+, homogenous strong HER2 IHC staining, high HER2/CEP17 ratio, and high HER2 copy number were significantly associated with pCR/RCB-I. In multivariate analysis, homogenous strong HER2 IHC staining pattern was significantly associated with pCR/RCB-I. The receiver operating characteristics (ROC) model showed either high HER2/CEP17 ratio or HER2 copy number individually was predictive of tumor response.

CONCLUSION

HER2 IHC staining pattern is significantly associated with tumor response to neoadjuvant chemotherapy, reiterating the importance of HER2 IHC evaluation. The ROC model shows either high HER2/CEP17 ratio or high HER2 copy number individually is predictive of tumor response to neoadjuvant HER2 targeted therapy in HER2+ breast cancer.