Purpose: Low physical functioning among breast cancer survivors appears to reduce survival, although the mechanisms underlying these associations are not clear. We examined inflammation as a possible biological mediator of association between low physical functioning and mortality after breast cancer.
Methods: Analysis included 2,892 participants from the Women's Healthy Eating and Living Study. All measures were collected at study baseline. Physical function was assessed by the Short Form 36 (SF-36) Health Survey Physical Function subscale. Low physical function was defined as the bottom tertile of the subscale score. Inflammation was measured as serum concentration of C-reactive protein (CRP). Cox proportional hazards modeled the associations of low physical function and the putative mediator (i.e., CRP) with all-cause and breast cancer-specific mortality.
Results: There were 293 deaths during study follow up, with 243 due to breast cancer. Low physical functioning was associated with a 50 % higher risk of all-cause mortality (HR, 1.49; 95 % CI, 1.2-1.9) and a 40 % higher risk of breast cancer-specific mortality (HR, 1.39; 95 % CI, 1.1-1.8), after adjustment for covariates. The addition of CRP did not markedly change the all-cause mortality hazard ratio attributed to low physical functioning. However, the addition of CRP modestly attenuated the breast cancer-specific mortality hazard ratio such that it was no longer statistically significant.
Conclusions: Interventions to improve physical functioning may prevent early morbidity and mortality among breast cancer survivors.
Implications for cancer survivors: Functional status measure may be a valuable indicator of long-term health outcomes among breast cancer survivors.