Pathological complete response in HER2 positive breast cancer treated with trastuzumab and chemotherapy: Predictive factors report.

Abstract

e12133 Background: Achieving a pathological complete response (pCR) in HER2 positive disease is a surrogate of survival. Several factors were studied in order to predict pCR, but only negative estrogen receptor is correlated to pCR. Methods: 168 patients (March 2002-December 2016) with neoadjuvant trastuzumab-based treatment were retrospectively analyzed in order to find if common clinicopathological factors, HER2 expression and immune infiltrates could correlate with pCR. Results: Median age was 55 years (29-86), median tumor size of 39mm and 53% of tumors had initial nodal involvement. 45% of patients were estrogen and 71% progesterone receptor negative and median ki67 expression was of 43%. Otherwise HER2 expression was analyzed by immunohistochemistry, FISH amplification and mRNA expression; we also determined the presence of immune infiltrates stromal and intratumoral L45 lymphocytes, PD1 and PD-L1. A 38% pCR rate was found in whole population. In the univariate model we found and association with pCR and: estrogen receptor negative (p = 0.003; OR 2.5), high HER2 expression by mRNA in tissue > 3.9 (p = 0.012; OR 8.4), stromal L45 expression > 35% (p = 0.001; OR 5.3), stromal PD1 expression > 10 (p = 0.004; OR 4.5). The most powerful factor associated with pCR is HER2 mRNA expression > 3.9, with 82% of pCR rate in those tumors; followed of L45 stromal expression > 35%, with 76% of pCR rate. Conclusions: Factors related to pCR are mostly estrogen receptor negative and high HER2 expression by mRNA and high L45 stromal infiltrates. With those variables, we could design a predictive model in order to perform the best neoadjuvant treatment to increase the pCR rate.