The spectrum of HER2 expression in breast cancer: linking immunohistochemistry quantification with in situ hybridization assay

Clinical and Biological Significance of HER2-Low in Ductal Carcinoma In Situ of the Breast

BACKGROUND

Ductal carcinoma in situ (DCIS) is the most common form of preinvasive breast cancer, with 5-10% of cases progressing into invasive disease. Herein, we investigated the association between HER2-low and clinico-pathological characteristics in DCIS and subsequent ipsilateral loco-regional relapse (LRR).

MATERIALS AND METHODS

We accessed our prospectively maintained institutional database. HER2 status was determined by immunohistochemistry and classified as null (score 0), over-expressed (3+), and low (1+ or 2+); in situ hybridization was not considered since it is not used for routine DCIS diagnostics.

RESULTS

Among 375 patients with DCIS, median age was 54 (27-88) years, with a primary tumor size < 2.5 cm in 63%, grade III in 33%, and positive hormone receptor status (HR) in 81% of cases; 71% underwent breast-conserving surgery, 34% received adjuvant endocrine and 39% radiotherapy. A total of 197 (52%) had tumors with low HER2 expression, which resulted significantly associated with grade I/II (P < .001), Ki67< 20% (P < .001), and HR-positive status (P < .001). HER2-low distribution varied from 19.61% and 50% in ER negative and ER-low (<10%) to 60% and 69% in ER high (50%-95%) and very high tumors (> 95%) (P < .001). After a median 39-month follow-up (IQR 16-65), cumulative incidences of LRR was 0.054. Among 17 patients with paired primary tumor and LRR, 5 had discordant HER2 status, with an even distribution of increased and decreased HER2 expression.

CONCLUSIONS

Low HER2 expression in DCIS is associated with features of reduced aggressiveness. Importantly, changes in HER2 expression may occur prompting retesting in recurrent cases, in line with observations in invasive breast cancer.

Comparison of breast cancer HER-2 receptor testing with immunohistochemistry and in situ hybridization

PURPOSE

Human epidermal growth factor receptor-2 (HER2) status can be tested with immunohistochemistry (IHC) and in situ hybridization (ISH). The 2018 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) HER2 testing guidelines suggest initial HER2 testing using IHC and further testing IHC equivocal cases with ISH. However, many institutions perform both IHC and ISH on the same specimen. This study aims to analyze the concordance between HER2 IHC and ISH in order to evaluate the benefit of repeating HER2 testing on the same breast cancer specimens.

METHOD

Patients diagnosed with invasive breast cancer through BreastScreen NSW Sydney West program between January 2018 and December 2020 were identified and their HER2 IHC and HER2 ISH results on core needle biopsy (CNB) and surgical excisions (SE) were retrospectively collected. Specimens with both IHC and ISH results were then analyzed for agreement and concordance using unweighted kappa values. Equivocal IHC (2+) cases were excluded from concordance analysis.

RESULTS

Overall, there were 240 invasive breast cancer specimens (CNB and SE) with both IHC and ISH recorded. Concordance between HER2 IHC and ISH was 100% (95% CI: 96.2-100%; κ = 1.00 (P < 0.001)). Of the IHC equivocal cases (n = 146), 94.5% were ISH negative.

CONCLUSION

There was perfect positive concordance and agreement between non-equivocal IHC and ISH results. This reinforces that IHC alone can be utilized reliably for testing HER2 status of non-equivocal cases consistent with the 2018 ASCO/CAP guidelines.

Exploring Real-World HER2-Low Data in Early-Stage Triple-Negative Breast Cancer: Insights and Implications

Purpose

This study aimed to compare the clinical behavior, clinicopathological and sociodemographic characteristics of patients with early-stage triple-negative breast cancer (TNBC) who belong to the HER2-low and HER2-zero subgroups.

Patients and Methods

This study involved a thorough search in the internal database of a single Brazilian institution to identify women with TNBC who underwent neoadjuvant chemotherapy (NACT) followed by curative surgery within the period from January 2010 to December 2014. HER2 analysis through immunohistochemistry (IHC) and, if required, amplification by in situ hybridization, was conducted using core biopsy samples. The study assesses outcomes of residual cancer burden (RCB), event-free survival (EFS), and overall survival (OS).

Results

A total of 170 cases were analyzed, with a mean age of 51.4 years (standard deviation, SD 11.2). The HER2 status was categorized as IHC 0, 1+, or 2+ in 80 (47.1%), 73 (42.9%), and 17 (10%) patients, respectively. No significant differences were observed in the prevalence of clinical pathological characteristics among the subgroups. The absence of significant results for clinicopathological and demographic features hindered the multivariate analysis of HER2 subgroups. Similarly, no significant differences were found in the RCB, EFS, and OS outcomes between HER2 subgroups.

Conclusion

The findings of this study suggest that, in early-stage TNBC, the clinical behavior and survival outcomes of the HER2-low subgroup may not differ significantly from those of the HER2-zero subgroup.

HEROHE Challenge: Predicting HER2 Status in Breast Cancer from Hematoxylin–Eosin Whole-Slide Imaging

Breast cancer is the most common malignancy in women worldwide, and is responsible for more than half a million deaths each year. The appropriate therapy depends on the evaluation of the expression of various biomarkers, such as the human epidermal growth factor receptor 2 (HER2) transmembrane protein, through specialized techniques, such as immunohistochemistry or in situ hybridization. In this work, we present the HER2 on hematoxylin and eosin (HEROHE) challenge, a parallel event of the 16th European Congress on Digital Pathology, which aimed to predict the HER2 status in breast cancer based only on hematoxylin–eosin-stained tissue samples, thus avoiding specialized techniques. The challenge consisted of a large, annotated, whole-slide images dataset (509), specifically collected for the challenge. Models for predicting HER2 status were presented by 21 teams worldwide. The best-performing models are presented by detailing the network architectures and key parameters. Methods are compared and approaches, core methodologies, and software choices contrasted. Different evaluation metrics are discussed, as well as the performance of the presented models for each of these metrics. Potential differences in ranking that would result from different choices of evaluation metrics highlight the need for careful consideration at the time of their selection, as the results show that some metrics may misrepresent the true potential of a model to solve the problem for which it was developed. The HEROHE dataset remains publicly available to promote advances in the field of computational pathology.