First Versus Second Primary Breast Cancer: A Surveillance, Epidemiology, and End Results-Based Comparison of Incidence, Treatment, and Survival

Background: First primary breast cancer (FPBC) and second primary breast cancer (SPBC) differ in clinical presentation, pathological features, molecular subtypes, and prognosis. This study compared the incidence, clinical characteristics, and survival outcomes of FPBC and SPBC from 2010 to 2021 using the Surveillance, Epidemiology, and End Results (SEER) database, and analyzed the impact of different treatment regimens on survival across patient subgroups. Methods: A total of 595,903 FPBC patients and 31,055 SPBC patients from the SEER database (2010–2021) were included in this study. The analysis focused on the incidence rates, demographic characteristics, and survival-related factors for both FPBC and SPBC. Additionally, the impact of different treatment regimens on survival was also evaluated. Results: Between 2010 and 2021, the incidence of SPBC showed a consistent increase, whereas the incidence of FPBC remained relatively stable, showing no significant upward or downward trend. SPBC patients exhibited a significantly worse survival prognosis compared with FPBC patients. Multivariate analysis identified age, race, marital status, year of diagnosis, tumor location, laterality, grade, SEER stage, histologic type, breast subtype, chemotherapy, surgery, radiation, and combination therapy as independent prognostic factors influencing long-term survival. The study also compared the impact of different treatment strategies on survival among FPBC and SPBC patients with varying clinical and demographic characteristics. Conclusions: This study demonstrates that SPBC patients have a significantly worse survival prognosis compared with FPBC patients. The poorer prognosis of SPBC is closely associated with pathological features, suboptimal treatment response, and the site of the prior primary cancer.