Dynamic body mass index trajectories predict survival outcomes in high-grade serous ovarian cancer: insights from a prospective cohort study

The prognostic role of body mass index (BMI) in ovarian cancer remains unclear. This study investigated nonlinear BMI associations with clinical outcomes and evaluated longitudinal BMI trajectory patterns in high-grade serous ovarian cancer (HGSOC). This prospective cohort study included 301 HGSOC patients treated at Xiangya Hospital between 2017 and 2020. BMI was measured at three standardized timepoints during treatment. Restricted cubic spline models assessed the relationship between BMI and progression-free survival (PFS), overall survival (OS), and platinum resistance. Group-based trajectory modeling identified distinct BMI patterns, and survival outcomes were analyzed with Cox regression. Random survival forest variable importance, parsimonious Cox sensitivity models, and treatment-strategy interaction tests were also performed. BMI showed U-shaped associations with PFS and platinum resistance, with an optimal BMI of 22–24 kg/m² ( P < 0.05; P for nonlinearity < 0.01). BMI was also linearly associated with OS, with lower BMI associated with higher mortality ( P < 0.05). Three BMI trajectories were identified: stable normal (56.1%), stable high (19.9%), and declining (23.9%). Both stable high and declining groups had significantly higher platinum resistance than stable normal (adjusted OR: 1.89 and 1.83, respectively; P < 0.01). The declining group had the poorest OS (adjusted HR: 1.51; 95% CI: 1.08–2.11), while the stable high group showed no significant difference. Parsimoniously adjusted PFS and OS estimates were consistent with the primary models, and no significant interaction was detected between treatment strategy and BMI trajectory for PFS (P for interaction = 0.389) or OS (P for interaction = 0.171). BMI showed a U-shaped association with disease progression and a linear association with OS in HGSOC. Longitudinal BMI analysis identified three patterns that provided complementary prognostic information, with declining trajectories associated with the poorest outcomes. These findings support systematic weight monitoring while requiring validation in contemporary treatment settings.