P5-13-23: Individualized Treatment Strategies for HER2−Negative Breast Cancer Subtypes.

Background Human epidermal growth factor receptor (HER2)-negative breast cancers are more heterogeneous than HER2−positive cancers, and tailored treatment is therefore required for luminal A and triple-negative breast cancer subtypes (LABC and TNBC). We therefore examined predictive factors for the efficacy of standard chemotherapy in LABC and TNBC subtypes. Methods A total of 109 LABC and 61 TNBC patients were treated with standard neoadjuvant chemotherapy (NAC) consisting of an anthracycline and/or taxane. The pathological treatment response and prognosis were examined for each subtype. Expression levels of the following factors were examined in association with quasi-pathological complete response (QpCR): estrogen- and progesterone-receptor (ER and PgR) status, HER2, nuclear grade, MIB-1, p53, topoisomerase IIα (topoIIα), cytokeratin (CK) 5/6 and epidermal growth factor (EGFR). Results QpCR rates in LABC and TNBC were 9.1% (10/109) and 54.1% (33/61), respectively. In LABC, the expression of PgR tended to be inversely associated with pathological response (p=0.087), while in TNBC, increased expression of topoIIa (p=0.006) and MIB-1 (p=0.018) were identified as predictors of QpCR. TopoIIα expression was also significantly associated with pathological response in multivariate analysis (p=0.014). The QpCR rate was higher in TNBC lacking CK5/6 and/or EGFR expression, defined as non-basal subtype (p=0.053). Conclusions Low expression of PgR may be a possible predictor of the efficacy of chemotherapy in LABC, while a high level of proliferative activity, indicated by topoIIa and MIB-1, is associated with chemosensitivity in TNBC. Further subclassification into basaland non basal-subtypes may also be helpful for the development of individualized treatments. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-13-23.