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.

Concordance between core needle biopsy and surgical excision for breast cancer tumor grade and biomarkers.

PURPOSE: Histopathological biomarkers guide breast cancer management. Testing histopathological biomarkers on both core needle biopsy (CNB) and surgical excision (SE) in patients who are treated with upfront surgery is unnecessary and costly if there is high concordance between the two. This study investigated the concordance between CNB and SE for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor-2 (HER2), tumor grade and Ki-67. METHODS: Histopathological biomarker information were retrospectively collected from preoperative CNB and SE on patients diagnosed with breast cancer through the BreastScreen Sydney West program over a four-year period between January 2017 and December 2020. Data were then analyzed to calculate percentage of agreement and concordance using kappa values for ER, PR, HER2, tumor grade and Ki-67. RESULTS: A total of 504 cases of invasive breast cancers were analyzed. There was substantial level of concordance for ER 96.7% (κ = 0.687) and PR 93.2% (κ = 0.69). Concordance for HER2 negative (IHC 0, IHC 1 +) or positive (IHC 3 +) tumor on CNB was 100% (κ = 1.00). Grade and Ki-67 showed moderate level of concordance, 72.6% (κ = 0.545) and 70.5% (κ = 0.453), respectively. CONCLUSION: ER, PR and HER2 show high level of concordance. CNB is reliable in determining histopathological biomarkers for ER, PR positive and HER2 positive or negative tumors indicating that retesting these on SE may not be necessary.