Prognostic Factors Affecting Survival of Patients With Single Primary Breast Cancer vs Patients With Multiple Primary Cancers in Lifetime, One of Which is Breast Cancer.

Purpose: The aim of this study was to investigate the demographic and molecular characteristics, overall survival (OS), cancer-specific survival (CSS), and prognostic factors affecting the survival of patients with single primary breast cancer (SPBC) and patients with multiple primary cancers in their life time in which one of them is breast cancer (MPC).

Methods: Using data from SEER 17 Research Plus, patients with breast cancer diagnosed between 2010 and 2019 were included in this study. Race, marital status, laterality, tumor size, molecular subtype, grade, stage, radiotherapy-chemotherapy treatment, and surgery data were analyzed in the data obtained after excluding patients with missing values. Kaplan-Meier survival analysis was used for survival analysis, and Cox regression analysis was used to evaluate the prognostic factors.

Results: 573175 patients were included in the study. The mean age of MPC patients was significantly higher than SPBC patients (65.99 ± 12.68, 60.33 ± 13.47, < .001, respectively). Patients with SPBC had significantly more hormone receptor (HR)-positive/Her2 positive, HR-negative/Her2-negative, and HR-negative/Her2-positive molecular subtypes; patients with MPC had more HR-positive/Her2-negative subtypes ( < .001). Grade 3 tumor status, locoregional spread, and distant metastasis were significantly higher in SPBC patients ( < .001). Overall survival and CSS rates were significantly higher in SPBC patients ( < .001). In MPC patients, overall hazard ratio was 1.631 times higher than SPBC, and the cancer-specific hazard ratio was 1.096 times higher (95% CI [1.606-1.656], 95% CI [1.071-1.121], respectively).

Conclusion: Although patients with SPBC have worse prognostic tumor characteristics, OS and CSS rates are better than patients with MPC.