Toward precision rehabilitation: a latent profile analysis of social support as a buffer against fatigue and reduced physical activity in breast cancer chemotherapy.

[PURPOSE] This study aimed to identify distinct patient subgroups based on co-evolving fatigue and physical activity trajectories during chemotherapy and to examine whether perceived social support independently predicts more favorable trajectory membership.

[METHODS] In a prospective longitudinal study, 226 patients with stage I-III breast cancer were assessed pre-, mid-, and post-chemotherapy. Cancer-related fatigue and moderate-to-vigorous physical activity were repeatedly measured. Baseline assessments included pre-diagnosis physical activity and perceived social support. Parallel-process latent profile analysis identified subgroups, and multinomial logistic regression examined predictors of membership.

[RESULTS] Three distinct profiles emerged: a "consistently high-functioning" profile (15.1%) with sustained high activity and low fatigue; a "vulnerable" profile (49.1%) with high fatigue and minimal activity; and an "adaptive" profile (35.8%) showing mid-treatment decline with recovery. After covariate adjustment, higher perceived social support was the sole modifiable factor specifically associated with consistently high-functioning profile membership (aOR = 1.188; 95% CI, 1.024-1.378). Younger age was also predictive.

[CONCLUSIONS] Patient adaptation during chemotherapy is highly heterogeneous. Perceived social support is a key determinant of the most favorable fatigue activity trajectory. Systematic assessment of social support at diagnosis may facilitate early risk stratification and inform targeted interventions to mitigate activity limitations and improve quality of life.