M. Kaur1, A. Quirarte2, A. Vertido3, T. Torosian3, T.M. Li3, J.A. Mouabbi4, R.A. Mukhtar2 1University of California, San Francisco, School Of Medicine, San Francisco, CA, USA 2University of California, San Francisco, Division Of Surgical Oncology, Department Of Surgery, San Francisco, CA, USA 3University of California, San Francisco, Department Of Surgery, San Francisco, CA, USA 4The University of Texas MD Anderson Cancer Center, Department Of Breast Medical Oncology, Houston, TX, USA
Introduction: Prior investigators have shown improved outcomes in patients with invasive lobular carcinoma (ILC) of the breast with concurrent lobular carcinoma in situ (LCIS) compared to ILC without LCIS. The impact of concurrent LCIS has not been evaluated in patients with pleomorphic ILC, a more aggressive subset of ILC with high risk of recurrence. We investigated the impact of concurrent LCIS on tumor characteristics and recurrence free survival (RFS) in both classic and pleomorphic ILC.
Methods: We retrospectively analyzed a prospectively maintained single-institution database of patients with stage I-III ILC. The impact on clinicopathologic characteristics (T and N stage, receptor subtype, grade, lymphovascular invasion), chemotherapy and surgery type (mastectomy, or lumpectomy), and RFS based on the presence of LCIS was analyzed in classic ILC and pleomorphic ILC. Multivariable Cox proportional hazards models were used to compare RFS.
Results: Of the 786 cases of ILC, 542 were classic and 92 were pleomorphic, with 70.6% overall having concurrent LCIS. Concurrent LCIS was more common in pleomorphic versus classic cases, although not statistically different (79.4% ILC/LCIS in pleomorphic versus 69.7% in classic, p=0.059). Overall, tumors with LCIS were less likely to be T3 (18.5% versus 25.9% T3 in tumors without LCIS, p=0.037) and had lower rates of advanced nodal involvement (9.1% versus 14.5% N2-3 in tumors without LCIS, p=0.026). Concurrent LCIS was associated with progesterone receptor (PR) positivity (83.5% versus 76.1% in ILC alone cases, p=0.016), and was more commonly grade 2 and less often grade 1 compared to ILC alone (70.4% grade 2 and 24.3% grade 1 versus 59.3% and 35.0%, respectively, in ILC alone, p=0.008). Treatment patterns differed, with ILC/LCIS cases more likely to undergo mastectomy (39.2% versus 28.0%, p=0.015). Additionally, patients with ILC/LCIS were less likely to receive chemotherapy (32.9% versus 41.9%, p=0.016), which was true for both classic (p=0.015) and pleomorphic ILC cases (p=0.013). There was no significant difference in RFS between those with and without LCIS in classic ILC, but among those with pleomorphic ILC, concurrent LCIS was associated with significantly improved RFS (Figure 1).
Conclusion: The presence of concurrent ILC/LCIS is associated with distinct tumor characteristics and treatment patterns. Overall, concomitant LCIS appears to convey a less aggressive phenotype of ILC (lower stage, more PR positivity). 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.