Histological type is not an independent prognostic factor for the risk pattern of breast cancer recurrences

Invasive lobular breast cancer (ILC) is less common than invasive ductal breast cancer (IDC) and appears to have a distinct biology. Inconsistent findings regarding disease-free survival (DFS) are probably due to the fact that histologic type is related to hormone receptor status. This study aims to determine whether the type of the primary breast cancer histology is an independent prognostic factor for DFS, the risk pattern of loco-regional recurrences and distant metastases (DM), and whether it is a prognostic factor for the site of DM. All Dutch women diagnosed between 2003 and 2005 with ILC (n = 2,949) or IDC (n = 22,378) were selected from the Netherlands Cancer Registry. DFS was assessed using proportional hazard regression analysis. Compared to patients with IDC, those with ILC were significantly older and more likely to have more than three positive lymph nodes and have larger, better differentiated, more multifocal, and hormone receptor positive tumors (all P < 0.001). ILC was more likely to metastasize to the gastrointestinal organs and bones and less likely to the lung, central nervous system, and lymph nodes. Within the ER+PR+ and ER+PR- subgroups ILC was still more likely to metastasize to gastrointestinal organs and less likely to the lung. The timing of recurrence was correlated to hormone receptor status, independent of histological type. Highest risks were observed among ER-PR- patients within 2 years of surgery. Multivariable analysis showed that histological type is not an independent significant prognostic factor of DFS for the first 3 years post-surgery and thereafter (< 3 years HR 0.91, 95 % CI 0.78-1.06, > 3 years HR 1.07, 95 % CI 0.88-1.30). Histological type should not be considered an important prognostic factor for the risk and risk pattern of recurrences.