Influence of histology on the effectiveness of adjuvant chemotherapy in patients with hormone receptor positive invasive breast cancer

Introduction: To investigate the effect of adjuvant chemotherapy on long term survival in addition to hormonal therapy in the systemic treatment of hormonal receptor positive breast cancer patients. Methods: All patients with primary non-metastatic hormonal receptor positive invasive lobular (mixed) (=ILC) and invasive ductal (=IDC) breast cancer operated on between 1986 and 2007 were identified from a population based cohort. Four hundred ninety-eight patients with lobular (mixed) and sixteen hundred seventeen with ductal cancer were eligible. Both groups were divided in patients receiving adjuvant hormonal treatment with or without systemic chemotherapy. Results: Overall survival was not statistically different in patients with ILC treated with adjuvant hormonal and chemotherapy compared to hormonal treatment alone (5-year survival 85.2% vs 82.8%, P = .68). In contrast, patients with IDC receiving adjuvant hormonal and chemotherapy had a significantly better overall survival compared to hormonal therapy alone (5-year survival rate 87.6% vs 80.8%, P <.001). In the multivariate analysis however, this significance disappeared suggesting that the data are possibly too small, too unbalanced, or influenced by other confounding factors to come to definitive conclusions. Conclusions: There are good reasons to consider ductal and lobular breast cancers as different entities in future studies. Patients with hormone receptor positive ILC seem to benefit differently from additional adjuvant chemotherapy to hormonal therapy as compared with patients with IDC.