The Effect of Marital Status on Suicide Risk Among Patients with Breast Cancer: A Population-Based sIPTW Competing Risk Analysis

Background: Breast cancer survivors often experience psychological distress that may increase suicide risk. Marital status, a proxy for social support, may influence this risk, but its role within a competing-risk framework is unclear. This study examined the association between marital status and suicide mortality and assessed modification by socioeconomic and geographic factors. Methods: This is a population-based cohort study using SEER data, including adults diagnosed with primary breast cancer from 2000 to 2022. Marital status was classified as married/partnered or unmarried/non-partnered. Baseline characteristics were balanced using subdistribution inverse probability of treatment weighting (sIPTW). Suicide mortality was analyzed using sIPTW-weighted Fine-Gray competing-risk models, treating non-suicide deaths as competing events. Landmark, subgroup, interaction, and sensitivity analyses were performed. Results: Among 825,047 patients, 40.7% were unmarried. Covariates were well balanced after weighting (SMD <0.01). During follow-up, 529 suicide deaths occurred. Unmarried status was associated with higher suicide mortality (sHR = 1.34, 95% CI: 1.12-1.60). Male sex and estrogen receptor-negative tumors increased risk, while older age and non-White race were protective. Findings were consistent in Cox models (HR = 1.45) and sensitivity analyses (sHR = 1.42). Landmark analyses showed persistent associations at 1, 3, and 5 years. The association was attenuated in the highest income quartile but not modified by rural-urban status. Conclusions: Unmarried breast cancer patients had higher suicide mortality. These findings support integrating psychosocial assessment and targeted suicide prevention into survivorship care, especially for socially vulnerable groups.