Depression, Anxiety, and the Risk of Cancer Incidence

Objectives
Depression, anxiety and other psychosocial factors are hypothesized to increase the risk of cancer through several biological mechanisms. We examined whether psychosocial factors interact with or modify the effects of health behaviors, such as smoking and alcohol use, in relation to cancer incidence.

Methods 
Two-stage individual participant data meta-analyses were performed based on 22 cohorts of the PSYchosocial factors and CAncer (PSY-CA) study. We examined nine psychosocial factors (depression diagnosis, depression symptoms, anxiety diagnosis, anxiety symptoms, perceived social support, loss events, general distress, neuroticism, relationship status), seven health behaviors/behavior-related factors (smoking, alcohol use, physical activity, body mass index, sedentary behavior, sleep quality, sleep duration) and seven cancer outcomes (overall cancer, smoking-related, alcohol-related, breast, lung, prostate, colorectal). We first estimated effects of the psychosocial factor, the health behavior and their product term on cancer incidence using Cox regression models within each cohort. Subsequently, cohort-specific effect estimates were pooled using multivariate random-effects meta-analyses. Additive and multiplicative interaction/effect modification were examined. 

Results 
This study involved 437,827 participants, 36,961 incident cancer diagnoses, and 4,749,481 person years of follow-up. Out of 756 combinations of psychosocial factors, health behaviors, and cancer outcomes, we found no evidence of interaction. Effect modification was found for some combinations, but there were no clear patterns for any particular psychosocial factors, health behaviors or cancer outcomes involved. 

Conclusion
We found no evidence for psychosocial factors to interact with health behaviors in relation to cancer incidence. The effects of health behaviors on cancer incidence are similar in people with and without depression, anxiety or psychosocial stress.