To investigate the impact of histologic type invasive lobular carcinoma (ILC) versus invasive ductal carcinoma (IDC) on response to primary chemotherapy (PC) and long-term outcome.

The study included 1,034 patients with stage II and III breast cancer who participated in six clinical trials of PC at our institution between 1985 and 2002. One hundred twenty-two patients (12%) had ILC and 912 (88%) had IDC. All patients received anthracycline-based PC, and 346 patients (33.5%) also received a taxane as part of PC. Pathologic complete response (pCR) was defined as no evidence of invasive disease in the breast and axillary lymph nodes.

The median patient age was 48 years (range, 18 to 79 years). Patients with ILC tended to be older (median age, 53 years v 47 years for patients with IDC) and have more hormone-receptor-positive tumors (92% v 62%; P < .001), lower nuclear grade (nuclear grade 3, 16% v 56%; P < .001), and higher stage at diagnosis (10% v 0% with stage IIIB or IIIC disease; P < .001). Patients with ILC were less likely to have a pCR (3% v 15%; P < .001) and had a larger number of involved axillary lymph nodes (41% v 26% had > 3 involved nodes; P = .001). At a median follow-up time of 70 months, ILC patients tended to have longer recurrence-free survival (P = .004) and overall survival (P = .001).

ILC is characterized by lower rates of pathologic response to PC but better long-term outcomes compared to IDC. pCR might not be a prognostic indicator for this group of patients.