Depression and anxiety were not associated with outcomes for most cancer types, including breast cancer, prostate cancer, and alcohol-related cancer, according to findings from a large, individual participant data meta-analysis.
An exception was for lung and smoking-related cancers, but key covariates appeared to explain the relationship between depression, anxiety, and these cancer types, the investigators reported.
The findings challenge a common theory that depression and anxiety increase cancer risk and should "change current thinking," they argue.
"Our results may come as a relief to many patients with cancer who believe their diagnosis is attributed to previous anxiety or depression," first author Lonneke A. van Tuijl, PhD, of the University of Groningen and Utrecht University, the Netherlands, noted in a press release.
Analyses included data from up to nearly 320,000 individuals from the 18 prospective cohorts included in the international Psychosocial Factors and Cancer Incidence (PSY-CA) consortium. The cohorts are from studies conducted in the Netherlands, United Kingdom, Norway, and Canada, and included 25,803 patients with cancer. During follow-up of up to 26 years and more than 3.2 million person-years, depression and anxiety symptoms and diagnoses showed no association with overall breast, prostate, colorectal, and alcohol-related cancers (hazard ratios, 0.98-1.05).
For the specific cancer types, the investigators "found no evidence for an association between depression or anxiety and the incidence of colorectal cancer (HRs, 0.88-1.13), prostate cancer (HRs, 0.97-1.17), or alcohol-related cancers (HRs, 0.97-1.06)."
"For breast cancer, all pooled HRs were consistently negative but mean pooled HRs were close to 1 (HRs, 0.92-0.98) and the upper limit of the 95% confidence intervals all exceeded 1 (with the exception of anxiety symptoms)," they noted.
An increase in risk observed between depression and anxiety symptoms and diagnoses and lung cancer (HRs, 1.12-1.60) and smoking-related cancers (HRs, 1.06-1.60), in minimally adjusted models, was substantially attenuated after adjusting for known risk factors such as smoking, alcohol use, and body mass index (HRs, 1.04-1.08), the investigators reported.
"Depression and anxiety have long been hypothesized to increase the risk for cancer. It is thought that the increased cancer risk can occur via several pathways, including health behaviors, or by influencing mutation, viral oncogenes, cell proliferation, or DNA repair," the authors explained, noting that "[c]onclusions drawn in meta-analyses vary greatly, with some supporting an association between depression, anxiety, and cancer incidence and others finding no or a negligible association."
The current findings "may help health professionals to alleviate feelings of guilt and self-blame in patients with cancer who attribute their diagnosis to previous depression or anxiety," they said, noting that the findings "also underscore the importance of addressing tobacco smoking and other unhealthy behaviors – including those that may develop as a result of anxiety or depression."
"However, further research is needed to understand exactly how depression, anxiety, health behaviors, and lung cancer are related," said Dr. Tuijl.
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