Clinical Outcomes Using Accelerated Partial Breast Irradiation in Patients With Invasive Lobular Carcinoma

Abstract

We compared clinical outcomes of women diagnosed with either invasive lobular carcinoma (ILC) or invasive ductal carcinoma (IDC) treated with accelerated partial breast irradiation (APBI). A total of 16 patients with ILC received APBI as part of their breast-conservation therapy (BCT) and were compared with 410 patients with IDC that received APBI as part of their BCT. Clinical, pathologic, and treatment related variables were analyzed including age, tumor size, hormone receptor status, surgical margins, lymph node status, adjuvant hormonal therapy, adjuvant chemotherapy, and APBI modality. Clinical outcomes including local recurrence (LR), regional recurrence (RR), disease-free survival (DFS), cause-specific survival (CSS), and overall survival (OS) were analyzed. Median follow-up was 3.8 years for the ILC patients and 6.0 years for the IDC patients. ILC patients were more likely to have positive margins (20.0% vs. 3.9%, p = 0.006), larger tumors (14.1 mm vs. 10.9 mm, p = 0.03) and less likely to be node positive (0% vs. 9.5%, p < 0.001) when compared with patients diagnosed with IDC. The 5-year rate of LR was 0% for the ILC cohort and 2.5% for the IDC cohort (p = 0.59). No differences were seen in the rates of RR (0% vs. 0.7%, p = 0.80), distant metastases (0% vs. 3.5%, p = 0.54), DFS (100% vs. 94%, p = 0.43), CSS (100% vs. 97%, p = 0.59), or OS (92% vs. 89%, p = 0.88) between the ILC and IDC patients, respectively. Additionally, when node-positive patients were excluded from the IDC cohort, no differences in the rates of LR (0% vs. 2.2%, p = 0.62), RR (0% vs. 0%), DFS (100% vs. 95%, p = 0.46), CSS (100% vs. 98%, p = 0.63), or OS (92% vs. 89%, p = 0.91) were noted between the ILC and IDC patients. Women with ILC had excellent clinical outcomes after APBI. No difference in local control was seen between patients with invasive lobular versus invasive ductal histology.