Survival analysis of metachronous bilateral ectopic breast cancer utilizing the SEER database and the pioneering construction of a nomogram model.

INTRODUCTION: Metachronous bilateral ectopic breast cancer (MBEBC) is clinically rare, but the incidence has been increasing in recent years and no clear therapeutic guidance or prognostic assessment is available. METHODS: Data on MBEBC patients from the Surveillance, Epidemiology, and End Results (SEER) database were gathered and randomly split into a training set and a validation set at a 7:3 ratio. Independent prognostic risk factors were identified through both univariate and multivariate analyses, and a nomogram was constructed based on these factors to predict survival outcomes. RESULTS: From the SEER database, we collected data on a total of 8240 patients spanning the years 2005-2015. These patients were then randomly divided into a training set (5768) and a validation set (2472) for analysis. The clinicopathological features indicated that Grade 2 tumors were the most prevalent, with invasive ductal carcinoma comprising 71.2% of the cases. Additionally, the majority of MBEBC patients were classified as N0, and only a small fraction (4.2%) exhibited distant metastases. A multivariate COX regression model was developed to identify independent prognostic risk factors for patients whose first and second tumors were both invasive ductal carcinomas, as well as those with more extensive pathological types. Nomograms were also constructed for survival prediction of overall survival (OS) and breast cancer-special survival (BCSS) at 3, 5, and 10 years. Receiver operating characteristic (ROC) curves were plotted and area under the curve (AUC) values were calculated. The AUC was greater than 0.7 in all models, with a 10-year OS of 78.0 (76.0-80.0) and a BCSS of 77.6 (76.0-79.3) in all patients. The calibration curves and decision curve analysis (DCA) demonstrate that the nomogram possesses strong clinical predictive capability and high predictive accuracy. CONCLUSION: This study detailed the clinicopathological characteristics of patients with the clinically rare MBEBC and identified independent prognostic risk factors across various pathology types. Additionally, a nomogram was developed for individualized prediction of patients' BCSS and OS, offering a new adjunctive tool for the clinical management of MBEBC patients.