Utility of Human Epidermal Growth Factor Receptor 2 (HER2) Retesting of Histologic Grade 3 Invasive Breast Carcinomas.

BACKGROUND: American Society of Clinical Oncology and College of American Pathologists guidelines recommend repeated evaluation of human epidermal growth factor receptor 2 (HER2) status on surgical specimens from patients with a diagnosis by core-needle biopsy of Grade 3, HER2-negative invasive tumors of the breast. However, there are limited data to support reflexive testing.

OBJECTIVE: To evaluate the utility of HER2 retesting of histologic Grade 3, HER2-negative invasive breast carcinomas.

METHODS: We evaluated 78 patients from Kaiser Permanente East Bay in whom Grade 3, HER2-negative invasive breast carcinoma was diagnosed between 2015 and 2017 by core biopsy, to compare HER2 status on core biopsy vs excisional biopsy specimen. The HER2 status was determined by immunohistochemistry, fluorescent in situ hybridization, or both. All patients were retested for HER2 status on surgical specimen according to the aforementioned guidelines. Recipients of neoadjuvant chemotherapy were excluded.

RESULTS: One of the 78 patients demonstrated negative-to-positive status discordance between core biopsy and surgical specimens and was treated with trastuzumab. One patient was HER2 negative by core biopsy and was HER2 equivocal by immunohistochemical and fluorescent in situ hybridization evaluation of the surgical specimen. Seventy-six patients demonstrated concordant HER2 status between core biopsy and surgical specimens.

CONCLUSION: The rate of clinically significant HER2 status discordance between core biopsy and surgical specimens in patients with Grade 3 breast carcinoma is low. However, given the dramatically improved survival conferred by trastuzumab therapy, our findings support reflex HER2 testing of surgical specimens for patients with core biopsy-diagnosed HER2-negative breast carcinoma.