Postoperative radiotherapy for invasive micropapillary carcinoma of the breast: an analysis of Surveillance, Epidemiology, and End Results database

Introduction: Invasive micropapillary carcinoma (IMPC) of the breast poses a high risk of locoregional recurrence, and postoperative radiotherapy (PORT) may be beneficial in IMPC. Hence, we determined the clinical value of PORT in IMPC patients. Patients and methods: We assessed clinicopathological factors extracted from the Surveillance, Epidemiology, and End Results database (2004-2013). Univariate and multivariate Cox proportional hazards regressions were performed to assess the independent prognostic factors on breast cancer-specific survival (BCSS) and overall survival (OS). Results: Of the 881 study patients, 444 (50.4%) and 437 (49.6%) underwent breast-conserving surgery (BCS) and mastectomy (MAST), respectively, of whom 357 (80.4%) and 153 (35.0%) underwent PORT, respectively. Patients with young age, large tumor size, or advanced nodal stage were more likely to undergo MAST and PORT compared with MAST alone. Patients with progesterone receptor-positive disease were more likely to receive BCS and PORT compared with BCS alone. The 5-year BCSS and OS were 95.7% and 90.9%, respectively. On multivariate analyses, tumor size, histological grade, and estrogen receptor status were independent predictors of BCSS and OS. The types of surgical procedures (MAST vs. BCS) were not an independent predictor of survival outcomes. Patients who underwent MAST with or without PORT had similar BCSS and OS in the multivariate analyses. Those who underwent BCS plus PORT did not have better BCSS and OS than those who underwent BCS alone. In the low-, intermediate-, and high-risk groups, PORT was not associated with better BCSS and OS than non-PORT groups in patients who received BCS or MAST. Conclusion: IMPC has favorable BCSS and OS. Regardless of the types of surgical procedures (MAST or BCS), PORT groups were not inferior to non-PORT groups on BCSS and OS.