Treatment and survival differences between patients with invasive lobular carcinoma versus invasive ductal carcinoma of the breast.

Background: Invasive lobular carcinoma (ILC) exhibits differences in molecular and biological characteristics compared to invasive ductal carcinoma (IDC). We aim to compare breast cancer-specific survival (BCSS) between patients with ILC and IDC.

Methods: We used data from the Surveillance, Epidemiology, and End Results database (1992-2020). Logistic regression analyses were conducted to identify factors associated with treatment modalities. We examined BCSS at different time points using a cox regression model with time-dependent coefficient.

Results: 343,397 patients with IDC and 39,859 patients with ILC were included. Patients with ILC had more advanced stage disease (stage II, 35% vs. 34%; stage III, 16% vs.11%), and higher rate of hormone receptor-positive disease (97% vs. 81%). Compared to patients with IDC, patients with ILC had better BCSS in the first five years (Hazard ratio [HR]=0.71, p <0.001), but worse BCSS in later years (HR=1.30, p<0.001 in year 6-10; HR=1.75, p<0.001 in year 11-15; HR=2.17, p<0.001 in year 16-20).

Conclusions: Patients with ILC survive better in early years but worse in later years compared to patients with IDC. Future studies are required to identify patients with ILC who are at risk of late recurrence or mortality.

Impact: The results of this study add to the currently conflicting literature of survival of ILC and demonstrate the importance of evaluating novel therapeutic approaches and extended therapy for patients with ILC.