Death by suicide and other externally caused injuries following a cancer diagnosis: The Japan public health center-based prospective study

Objective: There have been very few population-based prospective studies that have investigated the risks of deaths by suicide and other externally caused injuries (ECIs) among cancer patients in an Asian population. This study investigated whether the risk of death by both suicide and ECIs increases during the first year following the initial diagnosis of cancer. Methods: Data were analyzed from a population-based cohort of Japanese residents between 1990 and 2010, collected during the Japan Public Health Center-based Prospective Study. Poisson regression models were used to calculate adjusted risk ratios (RRs) for both suicide and ECI deaths. To adjust for unmeasured confounding factors, case-crossover analyses were conducted for all patients with cancer who died by suicide and ECIs. Results: A population-based cohort of 102,843 Japanese residents was established. During the follow-up period, there were 34 suicides and 48 ECI deaths among patients with cancer, as compared with 527 suicides and 707 ECI deaths among those who did not have cancer. Analyses revealed that those who were newly diagnosed with cancer were at a greatly increased risk of death by suicide and ECIs within the first year after their diagnosis (suicide RR = 23.9, 95% CI: 13.8-41.6; ECI RR = 18.8, 95% CI: 11.4-31.0). Furthermore, the case-crossover analyses generally confirmed the results of the Poisson regressions. Conclusions: The risks of suicide and ECI deaths within the first year after a cancer diagnosis were higher than those among cancer-free populations. A diagnosis of cancer is a critical experience that may increase the risk of fatal outcomes.