Invasive lobular carcinoma of the breast: local recurrence after breast-conserving therapy by subtype approximation and surgical margin.

Invasive lobular carcinoma (ILC) typically presents at a later stage than invasive ductal carcinoma (IDC) and poses unique radiographic and surgical challenges. However, current principles of breast-conserving therapy (BCT) do not distinguish between histologic subtypes, raising uncertainty about the optimal approach for patients with ILC. We studied 998 BCT patients from 1998-2007, comprised 74 % IDC, 8 % ILC, and 18 % with mixed ILC/IDC. In light of recent guidelines addressing surgical margins, specimens were assessed for margin width and biologic subtype. The Kaplan-Meier method and Cox proportional hazards models were used to analyze effects of patient and disease characteristics on local recurrence (LR). At a median of 119 months, 45 patients had an isolated LR. 10-year LR was 5.5 % for patients with IDC, 4.4 % for ILC, and 1.2 % for mixed histology (p = 0.08). The majority of ILC cases had luminal A biologic subtype (91.1 %), and analysis among all luminal A cases revealed 10-year LR of 2.6 % for IDC, 3.4 % for ILC, and 0 % for mixed tumors (p = 0.12). Patients with ILC were more likely to have initially positive surgical margins (45.0 vs 17.5 %; p < 0.001) resulting in more frequent re-excision (57.1 % vs 40.4 %; p = 0.02), though final margins were similar between ILC and IDC (p = 0.88). No LR was observed among ILC or mixed histology patients with margins <2 mm (n = 28). On multivariate analysis, histologic subtype was not associated with LR (p = 0.52). Modern approaches confer similarly favorable LR rates for ILC, IDC, and mixed histology breast cancers despite inherent histologic differences. Patients with ILC did not require more extensive surgical margins than those with IDC.