Abstract The Surveillance, Epidemiology, and End Results (SEER) Program was used to compare survival and local recurrence risk (LR) in patients with 2 histologic types of disease—invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC)—receiving breast-conserving surgery (BCS). Patients with T1-2 ILC were less likely to undergo BCS and had better overall survival compared to patients with IDC, but they had worse second primary cancer-free survival and higher LR than those of patients with IDC in the nuclear grade III subgroup. Continuing efforts to identify a subset of subjects with T1-2 ILC of nuclear grade III is contraindicated for BCS in further clinical trials. Background: The role of histology subtype on the prognosis of T1-2 breast cancer patients receiving breastconserving surgery (BCS) is not clear. Methods: The Surveillance, Epidemiology, and End Results (SEER) Program was used to compare overall survival, second primary cancer-free survival (CFS), and local recurrence risk (LR) for patients with invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC), both receiving BCS. Results: The study enrolled 196,688 patients with T1-2 disease receiving BCS, including 12,906 with ILC and 183,782 with IDC. Patients with IDC showed higher unadjusted annual rates of BCS than ILC. Five- and 10-year estimated survival rates were, respectively, 92.06% and 86.14% in ILC, compared to 90.50% and 85.26% in IDC (P ?.12). In multivariable Cox regression, ILC patients showed advantage over IDC in overall survival (hazard ratio [HR] ?0.93, P ?.001), whereas no significant differences in CFS (HR ?1.03, P ?.33) and LR (HR ?1.17, P ?.06) were found, which were consistent with results from matched cohort. In subgroup analyses, patients with grade III ILC had poorer CFS (HR ?1.23, P ?.009) and higher LR (HR ?1.59, P ?.01) than IDC. Conclusion: Histologic type is of prognostic importance in T1-2 patients receiving BCS, and surgeons should be cautious in performing BCS for individuals with grade III ILC.