Is survival from infiltrating lobular carcinoma of the breast different from that of infiltrating ductal carcinoma?

Previous studies of patients with breast cancer have compared survival of invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) with contradictory results. This study examines the effect of the diagnosis of IDC or ILC in conjunction with age at diagnosis, pathologic tumor size, pathologic stage, histologic grade, and lymph node status of 307 women with IDC or ILC in 1992 in the Greater Western region of Sydney in Australia. Survival analysis was conducted using the Kaplan-Meier method. Relative risks associated with IDC or ILC and other important prognostic factors and adjusted for each other were computed using Cox proportional hazard regression. The proportion of grade I tumors was significantly higher in ILC (41%) than in IDC (16%). Conversely, the proportion of grade III tumors was only 18% in ILC as against 41% in IDC (p = 0.020). The 10-year survival of women with IDC was 69%, compared to 84% for ILC (p = 0.073). However, the 15 percentile point difference between overall survival of IDC and ILC was markedly reduced after adjustment for nodal status. The difference was eight percentile points for node-negative patients (p = 0.361) and five percentile points for node-positive patients (p = 0.464). Age at diagnosis, tumor size, pathologic stage, and lymph node status were independent prognostic indicators for 10-year survival. There was no prognostic difference between IDC and ILC. The result shows the importance of adjusting for other important clinicopathologic characteristics before comparing the overall survival of IDC and ILC.