Tumor characteristics and patient outcomes are similar between invasive lobular and mixed invasive ductal/lobular breast cancers but differ from pure invasive ductal breast cancers

Background: The aim of this study was to investigate the clinical characteristics associated with invasive lobular cancer (ILC) and mixed invasive ductal cancer (IDC) and ILC compared with IDC. Methods: From 1996 to 2006, 4,336 patients with IDC, ILC, and mixed breast cancers were identified. Clinical variables were compared using χ² and Fisher's exact tests. Kaplan-Meier survival curves were constructed. Results: Patients included 3,595 (83%) with IDC, 480 (11%) with ILC, and 261 (6%) with mixed cancers. Patients with ILC and mixed cancers were more likely to have low-grade and estrogen-positive and progesterone-positive tumors but were diagnosed at higher stages of disease compared with patients with IDC (P < .05 for each). Patients with IDC had the poorest 5-year (80%) and 10-year (61%) survival compared with patients with ILC (87% and 68%) and mixed (84% and 69%) cancers (P = .029). Conclusions: Although patients with ILC and "mixed" cancers are diagnosed with more advanced disease, their survival is superior to patients with IDC.