The Association of Neoadjuvant Systemic Treatment on Hormone Receptor and Her2 Expression in Breast Cancer

Background: Pathological complete response (pCR) following neoadjuvant systemic treatment(NAST) for breast cancer is associated with improved prognosis; however, a large proportion of patients have residual disease. Oestrogen Receptor (ER) and HER2 status have been shown to affect likelihood of achieving pCR, with ER positive tumors being more treatment resistant. As hormone receptor status is heterogeneous within tumors, we postulated that, following NAST, ER expression would change in patients with residual disease, as the ER negative cells within the tumor are more treatment sensitive. Methods: A retrospective case series of patients treated with NAST prior to surgery at our institution was conducted. Information collected included demographic data, tumor grade, hormone receptor and HER2 status both before and after treatment, and pCR rates. Results: Of the 44 patients included, half achieved pCR. HER2 status (P=0.01), and subtype (P=0.008) were significantly associated with pCR. HER2 positive/ER negative tumors were most likely to undergo pCR. Approximately 80% of residual disease was ER positive. Higher levels of ER expression were also associated with increasing residual cancer burden (RCB) class (P=0.037). There was no trend between change in ER or HER2 expression following NAST. Median change in ER expression was 80% to 90% (P= 0.89), HER2 intensity changed from 3.0 to 2.2 (P=0.67) following treatment. Conclusion: Consistent with the literature, we have shown associations between ER and HER2 status and PCR, and between ER expression and residual disease burden. Our study was not able to demonstrate a significant trend in hormone and HER2 expression