Suicide attempt and future risk of cancer: a nationwide cohort study in Sweden

Little is known about cancer incidence among patients with a history of suicide attempt. Suicide attempters have lower levels of oxytocin, a hormone related to lactation, stress, social functioning, and well-being, and recent research indicates influence on carcinogenesis. We hypothesized that the low oxytocin levels among suicide attempters results in an increased risk of cancer in general and in organs with oxytocin receptors in particular. A nationwide cohort study of patients aged 15 years or older with hospitalization for self-inflicted injury or attempted suicide was identified from the Swedish patient register in 1968-2011. The cancer outcomes were identified from the Swedish cancer register. Cancer risk in suicide attempters was compared with the risk in the background population of the corresponding age, sex, and calendar period by calculating standardized incidence ratios (SIRs) with 95 % confidence intervals (95 % CI). The 186,627 patients (83,637 men and 102,990 women) hospitalized for self-inflicted injury or attempted suicide contributed with 2.6 million person-years at risk. The SIR for all cancer was 1.3 (95 % CI 1.27-1.33) in men and 1.25 (1.22-1.28) in women. For cancers in organs rich in oxytocin receptors (uterus, breast, and brain), the corresponding SIRs were 1.02 (0.87-1.19) and 1.13 (1.09-1.17), respectively. There was a particularly increased risk of cancers related to alcohol and tobacco in both sexes. Patients attempting suicide have an increased risk of cancer. However, this increase does not seem to be associated with low oxytocin levels, but rather to exposures like tobacco smoking and alcohol consumption.