Invasive lobular vs. ductal breast cancer: a stage-matched comparison of outcomes.

Background: Invasive lobular breast cancer (ILC) is less common than invasive ductal breast cancer (IDC), more difficult to detect mammographically, and usually diagnosed at a later stage. Does delayed diagnosis of ILC affect survival? We used a national registry to compare outcomes of patients with stage-matched ILC and IDC.

Methods: Query of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) tumor registry identified 263,408 women diagnosed with IDC or ILC between 1993 and 2003. Survival of patients matched by T and N stage was compared using Kaplan-Meier curves and log-rank analysis.

Results: When compared with IDC, ILC was more likely to be >2 cm (43.1 vs. 32.6%; P < 0.001), lymph node positive (36.8 vs. 34.4%; P < 0.001), and ER positive (93.1 vs. 75.6%; P < 0.001). The 5-year disease-specific survival (DSS) was significantly better for patients with ILC than for those with IDC, before (90 vs. 88%; P < 0.001) and after matching for stage T1N0 (98 vs. 96%; P < 0.001), T2N0 (94 vs. 88%; P < 0.001), and T3N0 (92 vs. 83%, P < 0.001). The 5-year DSS for patients with nodal metastasis of ILC vs. IDC was 89% vs. 88% (P = NS) for stage T1N1, 81 vs. 73% (P < 0.001) for T2N1, and 72 vs. 56% (P < 0.001) for T3N1. Multivariate analysis identified a 14% survival benefit for ILC (hazard ratio 0.86, 95% confidence interval 0.80-0.92).

Conclusions: Stage-matched prognosis is better for patients with ILC than for those with IDC. Our findings support a different biology for ILC and are important for counseling and risk stratification.