Post-Mastectomy Radiation Therapy for Invasive Lobular Carcinoma: A Comparative Utilization and Outcomes Study

To date, there have been no analyses to assess factors that influence post-mastectomy radiation therapy (PMRT) utilization in invasive lobular carcinoma (ILC) or to quantify the benefit of PMRT in ILC as compared with invasive ductal carcinoma (IDC). We compared histology-specific utilization of PMRT by tumor and patient characteristics and estimated the effect of PMRT on overall and breast cancer-specific survival in ILC and IDC patients meeting American College of Radiology (ACR) criteria for PMRT.

We used the Surveillance, Epidemiology, and End Results database to identify women diagnosed with ILC or IDC from 2004 to 2009 who underwent mastectomy. We assessed utilization of PMRT by T and N stage, analyzed factors associated with PMRT use, and quantified the histology-specific survival benefit of PMRT using log-rank tests and multivariate Cox regression analysis.

We identified 86,098 IDC and 12,703 ILC patients. Within this cohort, 18.7% of IDC patients and 26.1% of ILC met ACR criteria for PMRT. Among patients with a definite indication, PMRT was more commonly employed in ILC than in IDC (59.6% vs. 56.3%; P = .0004). Among patients with a definite indication for PMRT, radiation improved 5-year breast cancer-specific survival from 71.4% to 77.0% for IDC (P < .0001) and from 80.9% to 84.7% for ILC (P = .0003).

PMRT was used more commonly in ILC than in IDC. PMRT significantly improves 5-year overall survival and breast cancer-specific survival for ILC patients to a degree comparable with that seen in IDC. Moreover, among ILC and IDC patients who meet ACR criteria, PMRT appears to be significantly underutilized.