Impact of concurrent lobular carcinoma in situ on recurrence outcomes in patients with classic and pleomorphic invasive lobular carcinoma of the breast

Abstract Purpose We investigated outcomes of invasive lobular carcinoma (ILC) with or without concurrent lobular carcinoma in situ (LCIS) in patients with classic or pleomorphic ILC. Methods We retrospectively analyzed a single-institution database of patients with stage I-III ILC. We compared tumor features, treatment, and recurrence free survival (RFS) in patients with ILC-alone versus ILC + LCIS stratified by ILC tumor subtype. Multivariable Cox proportional hazards models were used for multivariate analysis. Results Of the 786 cases of ILC, 542 were classic and 92 were pleomorphic, with 70.6% overall having concurrent LCIS. Overall, ILC + LCIS cases were less often T3 (p = 0.037) and had lower rates of N2/N3 disease (p = 0.026) than ILC-alone. Concomitant LCIS was also associated with greater progesterone receptor (PR) positivity (p = 0.016), and was more commonly grade 2 and less often grade 1 compared to ILC-alone (p = 0.008). Treatment differed, with ILC + LCIS cases receiving less chemotherapy (p = 0.016) and more mastectomy (p = 0.015). Among patients with classic ILC, the presence of concomitant LCIS was not associated with different RFS. However, among those with pleomorphic ILC, ILC + LCIS was associated with significantly improved RFS compared to ILC-alone (HR 0.31, 95% confidence interval 0.10–0.96, p = 0.043). Conclusion While the presence of LCIS was not associated with RFS in classic ILC in this dataset, it is a favorable prognostic factor in pleomorphic ILC, suggesting a potentially differential role in ILC subtypes.