Incidence of and Factors Associated With Nonfatal Self-injury After a Cancer Diagnosis in Ontario, Canada

IMPORTANCE: Psychological distress is a key component of patient-centered cancer care. While a greater risk of suicide among patients with cancer has been reported, more frequent consequences of distress, including nonfatal self-injury (NFSI), remain unknown. OBJECTIVE: To examine the risk of NFSI after a cancer diagnosis. DESIGN, SETTING, AND PARTICIPANTS: This population-based retrospective cohort study used linked administrative databases to identify adults diagnosed with cancer between 2007 and 2019 in Ontario, Canada. EXPOSURES: Demographic and clinical factors. MAIN OUTCOMES AND MEASURES: Cumulative incidence of NFSI, defined as emergency department presentation of self-injury, was computed, accounting for the competing risk of death from all causes. Factors associated with NFSI were assessed using multivariable Fine and Gray models. RESULTS: In total, 806 910 patients met inclusion criteria. The mean (SD) age was 65.7 (14.3) years, and 405 161 patients (50.2%) were men. Overall, 2482 (0.3%) had NFSI and 182 (<0.1%) died by suicide. The 5-year cumulative incidence of NFSI was 0.27% (95% CI, 0.25%-0.28%). After adjusting for key confounders, prior severe psychiatric illness, whether requiring inpatient care (subdistribution hazard ratio [sHR], 12.6; 95% CI, 10.5-15.2) or outpatient care (sHR, 7.5; 95% CI, 6.5-8.8), and prior self-injury (sHR, 6.6; 95% CI, 5.5-8.0) were associated with increased risk of NFSI. Young adults (age 18-39 years) had the highest NFSI rates relative to individuals aged 70 years or older (sHR, 5.4; 95% CI, 4.5-6.5). The magnitude of association between prior inpatient psychiatric illness and NFSI was greatest for young adults (sHR, 17.6; 95% CI, 12.0-25.8). Certain cancer subsites were also associated with increased risk, including head and neck cancer (sHR, 1.5; 95% CI, 1.2-1.9). CONCLUSIONS AND RELEVANCE: In this study, patients with cancer had a higher incidence of NFSI than suicide after diagnosis. Younger age, history of severe psychiatric illness, and prior self-injury were independently associated with risk of NFSI. These exposures appeared to act synergistically, placing young adults with a prior mental health history at the greatest risk of NFSI. These factors should be used to identify at-risk patients.