Background
Cancer is a life-altering event causing considerable psychological distress. However, population-representative variations in the total burden of psychiatric episodes across cancer types and treatment modalities have not been examined. We sought to estimate the risk of self-harm after incident psychiatric disorder diagnosis in patients with cancer, and the risk of unnatural deaths after self-harm.
Design, Setting, Participants
Population-based cohort study with multiphase study designs. Population-based linked patient records in England (1998-2020) from primary care practices, hospitals, cancer registry and death registry were employed. We identified 459,542 individuals age ≥ 18 years with an incident diagnosis of a site-specific cancer of interest.
Main outcome measures
Using outpatient and inpatient records, we identified patients with five psychiatric disorders of interest: depression, anxiety disorder, schizophrenia, bipolar disorder and personality disorder. Cumulative burden for all psychiatric events was estimated using the mean cumulative count method. We considered 10 cancer treatment regimens, 11 chemotherapy drug classes, deprivation status and 21 non-cancer comorbidities in stratified analyses. Propensity score matching was employed to identify controls who did not have any record of a psychiatric disorder of interest. For each psychiatric disorder category, we fitted a Cox regression model to estimate the risk of self-harm. We also estimated the risk of all-cause mortality and excess years of life lost comparing patients with and without psychiatric disorders. A separate matched cohort was generated to explore the risk of suicide and unnatural deaths following self-harm.
Results
Depression was the most common psychiatric disorder in patients with cancer, where some of the highest cumulative burdens were observed in patients with testicular cancer (98.05 per 100 individuals [CI: 83.08-127.25]), cervical cancer (78.74 [73.61-90.14]) and Hodgkin lymphoma (69.87 [61.05-69.48]) by age 60. Patients who received chemotherapy, radiotherapy and surgery had the highest cumulative burden of psychiatric disorders, while patients who received radiotherapy alone had the lowest burden. Patients treated with alkylating agent chemotherapeutics had the highest burden of psychiatric disorders while those treated with kinase inhibitors had the lowest burden. Among patients with cancer, 5,683 individuals were identified as having an incident self-harm episode. A previous diagnosis of psychiatric disorder before self-harm was at least twice as prevalent than a subsequent diagnosis of psychiatric disorder where the prevalence ratio was the highest in patients with brain tumours (5.36, CI: 4.57-6.14). Younger individuals were more likely to be diagnosed with mental illness before the first self-harm episode. However, individuals from more deprived regions (2.46, CI: 2.32-2.60) and individuals with ≥4 pre-existing comorbidities (2.19, CI: 1.92-2.46) were less likely to be diagnosed with mental illness before self-harm. Patients with mental illness had a higher cumulative burden of self-harm events compared with matched controls. All mental illnesses were associated with an increased risk of subsequent self-harm, where the highest risk was observed within 12 months of the mental illness diagnosis. Risks of self-harm during the first year in matched cohorts were as follow: depression (adjusted HR 44.1, CI: 34.0-57.1), anxiety disorder (HR 21.1, CI: 16.4-27.0) and schizophrenia (HR 7.5, CI: 5.0-11.2). Patients with cancer and psychiatric disorder experienced excess years of life lost. Patients who harmed themselves were 6.8 times more likely to die of unnatural causes of death compared with controls within 12 months of self-harm (HR 6.8, CI: 4.3-10.7). The risk of unnatural death after 12 months was markedly lower (HR 2.0, CI: 1.5-2.7).
Conclusions
This study quantifies the total burden of psychiatric events and self-harm in patients with cancer. The cumulative burden of psychiatric events varies across cancer type, treatment regimen and chemotherapy type. Incident psychiatric disorder diagnoses were significantly associated with increased risk of subsequent self-harm, where risks varied across psychiatric diagnostic categories and follow-up periods. Patients who harm themselves experienced the highest risk of dying from unnatural deaths within the first year of self-harm. We provide an extensive knowledge base to help inform collaborative cancer-psychiatric care initiatives by prioritising patients who are most at risk.
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