Kalliopi Siziopikou, MD, PhD
For the past 2 decades, clinical guidelines for the diagnosis and management of breast cancer have sought to clarify the definition of HER2 status, but several key questions remain, Kalliopi Siziopikou, MD, PhD, said in a presentation at the 2019 Lynn Sage Breast Cancer Symposium.1
Clinical question 2 asked whether HER2 testing of a surgical specimen must be repeated if the initial core biopsy was negative. The answer, according to the guidelines is, “If the initial HER2 test result in a core needle biopsy specimen of a primary breast cancer is negative, a new HER2 test may be ordered on the excision specimen.”
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Siziopikou explained that IHC HER2-negative cases are generally accurate and do not need repeating on excisions. She noted several possible exceptions, such as the possibility of repeating IHC when the tumor is histologic grade 3, a small amount of high-grade tissue is present on the core, or the resection contains a high-grade component not present on the core. Conversely, the guidelines instruct not to repeat IHC when the tumor is histologic grade 1; infiltrating ductal or lobular carcinoma is strongly estrogen receptor/progesterone receptor positive; or tubular, mucinous, or cribriform carcinoma is >90% pure.
Clinical questions 3 to 5 all elicited the same answer: “[A] definitive diagnosis will be rendered based on additional [work-up].” Clinical question 3 asked whether invasive cancers with a HER2 enumeration probe 17 (CEP17) ratio of ≥2 should be considered ISH positive, especially given that the average HER2 signals per cell is <4.
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