Abstract Background: De novo metastatic breast cancer (MBC) presents distinct clinical challenges and accounts for a small proportion of all breast cancer cases. While extensive data exist for female patients, the characteristics and outcomes of male patients with de novo MBC remain poorly defined. Comparing clinicopathological features and prognoses between male and female patients may help improve personalized management strategies for this rare subgroup. In this study, we compared the clinicopathological features and prognoses of male and female patients diagnosed with de novo metastatic breast cancer. Method: This retrospective study utilized data from the Surveillance, Epidemiology, and End Results (SEER) database, including male and female patients diagnosed with de novo metastatic breast cancer, between 2000 and 2021. Demographic and clinicopathological variables were collected to compare baseline characteristics. Survival outcomes were assessed using Kaplan-Meier analysis, and multivariate Cox regression was performed to identify independent prognostic factors. Statistical analyses were conducted using SPSS version 30.0. Results: A total of 60,590 patients met the study criteria. Of these patients, 713 (1.2%) were male. 56.1% were under 65 years of age. Pathological subtypes were HR+/HER2- (61.2%), HR+/HER2+ (15.9%), HR-/HER2- (14.3%), and HR-/HER2+ (8.6%). All patients had de novo metastatic disease. Metastatic sites were bone (64.2%), lung (30%), distant lymph node (27%), liver (24.2%), brain (7.3%), and other (18%). At the time of diagnosis, statistically significant differences were detected in patient groups in terms of age (p0.001), marital status (p0.001), origin (p0.001), race (p0.001), histologic type (p0.001), breast cancer subtype (p0.001), liver metastasis (p0.001), lung metastasis (p0.001) 5-year survival of de novo metastatic female breast cancer patients was found to be better than male patients (31.4% vs. 25.6%, p = 0.036). Conclusions: Male breast cancer is quite rare. The clinicopathological features and metastatic spread of male and female patients at diagnosis differ. Female patients were found to have a better survival rate. Citation Format: I. Dogan, A. Azizy, I. D. Subası, I. Yıldız, A. Arican, S. Yücel, O. Dülgeroğlu, M. Bozkurt, C. Uras. Comparison of Clinicopathological Features and Prognoses in Male and Female Patients with Denovo Metastatic Breast Cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-09-11.
Doğan et al. (Tue,) studied this question.