Increased Risk for Ipsilateral Breast Tumor Recurrence in Invasive Lobular Carcinoma after Accelerated Partial Breast Irradiation Brachytherapy.

BACKGROUND The suitability criteria for accelerated partial breast irradiation (APBI) from the American Brachytherapy Society (ABS), American Society of Therapeutic Radiology and Oncology (ASTRO), and the European Society for Radiotherapy and Oncology (GEC-ESTRO) have significant differences. MATERIALS AND METHODS This is a single institution retrospective review of 946 consecutive patients with invasive breast cancer who underwent lumpectomy and APBI intracavitary brachytherapy from 2003 to 2018. Overall survival (OS), breast cancer-specific survival (BCSS), relapse-free survival (RFS), and ipsilateral breast tumor recurrence (IBTR) were estimated with Kaplan-Meier method. RESULTS Median follow-up time was 60.2 months. Median age was 68 years (46-94 years). The majority of patients had estrogen receptor (ER)-positive disease (94%). There were 821 (87%) cases of invasive ductal carcinoma and 68 cases (7%) of invasive lobular carcinoma (ILC). The 5-year OS, BCSS, RFS, and IBTR was 93%, 99%, 90%, and 1.5%, respectively. Upon univariate analysis, ILC (HR 4.6, p=0.008) and lack of nodal evaluation (HR 6.9, p=0.01) were risk factors for IBTR. The 10-year IBTR was 2.5% for IDC and 14% for ILC. Patients deemed unsuitable by the ABS or ASTRO criteria, or high risk by the ESTRO criteria, were not at increased risk for IBTR or RFS. CONCLUSIONS These results show that APBI is an effective treatment for patients with invasive breast cancer. Expansion of the current eligibility criteria should be considered, though prospective validation is needed. Caution is required when considering APBI for patients with ILC. IMPLICATIONS FOR PRACTICE In a large retrospective review of 946 patients with early breast cancer treated with partial mastectomy and APBI intracavitary brachytherapy, we demonstrate durable local control. Patients deemed unsuitable or high risk by the American Brachytherapy Society, American Society of Therapeutic Radiation Oncology, and European Society for Radiotherapy and Oncology guidelines were not at increased risk for IBTR, suggesting that expansion of the current criteria should be considered. Importantly, however, our results demonstrate that caution should be taken when considering APBI for patients with invasive lobular carcinoma, as these patients had relatively high risk for IBTR (10-year IBTR 14%).