Epidemiology, Treatment and Prognosis Analysis of Small Cell Breast Carcinoma: A Population-Based Study.

Background: Primary small cell breast carcinoma (SCBC) is an uncommon malignancy with highly invasive behavior. The aim of this study was to find out more about the incidence, clinicopathologic characteristics and identify potential prognostic factors of SCBC. Methods: Data of patients with primary diagnosis of SCBC between 1975 and 2018 were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. The incidence after adjustment for age and percentage change per year in incidence were calculated. Disease-specific survival (DSS) and overall survival (OS) were analyzed among these SCBC patients identified from the SEER database. The whole cohorts were randomized into training and validation cohorts as ratio of 7: 3. Cox regression analysis was performed to determine predictors of survival with the training cohorts. Predictive models were constructed with training cohorts, and nomogram validation was performed using receiver operating characteristic curves, concordance indices and calibration curves in both training and validation cohorts. Results: 323 SCBC patients were enrolled finally during the research period. The overall incidence after adjustment for age between 1990 and 2018 was 0.14 per million per year, and the prevalence of the incidence has plateaued. Most of these tumors were poorly differentiated or undifferentiated. The most prevalent presenting stage was Stage II. Patients identified in this study were randomly divided into training (n = 226) and testing (n = 97) cohorts. Multivariate Cox proportional hazards model showed that chemotherapy, surgery and stage were important predictors of DSS and OS. Conclusion: SCBC is considered an infrequent breast neoplasm with aggressive characteristics. Tumor stage is associated with poor prognosis. Combination of surgery and chemotherapy is the main treatment for SCBC.