Primary breast lymphoma in males: Incidence, demographics, prognostic factors, survival, and comparisons with females.

Background: Primary breast lymphoma (PBL) is a rare disease condition and is mainly observed in females. No male PBL cohorts were reported previously. This study aims to investigate the incidence, clinical characteristics, prognostic factors, and survival outcomes among male PBL patients and also to perform comparisons between males and females.

Methods: Patients diagnosed with PBL between 2000 and 2019 from the Surveillance, Epidemiology, and End Results (SEER) database were identified. Age-adjusted incidence rates were calculated by year and age for trend analysis. Univariate and multivariate Cox hazard proportional regression analyses were performed to identify prognostic factors. Survival comparisons were conducted using the Kaplan-Meier method and the log-rank test. The propensity matching score (PSM) method was used to balance demographics.

Results: The incidence rate of 122 male PBL patients diagnosed in the period of 2000 to 2019 was 0.169 (95% CI: 0.140-2.203) per million persons, which was much lower than that of 2,543 females (1.59, 95% CI: 1.53-1.65). Clinical demographics were similar between females and males, except for lymphoma subtype distribution ( = 0.025). A higher age [hazard ratio (HR) = 1.08, 95% CI: 1.05-1.12,  < 0.001] and not receiving radiotherapy (receiving vs. not receiving: HR = 0.41, 95% CI: 0.21-0.78,  = 0.007) were significant risk factors associated with overall survival (OS) in males. Radiotherapy (OS:  = 0.023) can offer benefits in OS. Using the PSM method, we also revealed that male PBL patients had significantly worse OS and cancer-specific survival rates than females.

Conclusions: This study first analyzed male patients with PBL involving incidence, clinical characteristics, and survival data. Sex disparity was also observed in the survival outcome of the disease.