The effect of a severe psychiatric illness on colorectal cancer treatment and survival: A population-based retrospective cohort study

Objectives To identify inequalities in cancer survival rates for patients with a history of severe psychiatric illness (SPI) compared to those with no history of mental illness and explore differences in the provision of recommended cancer treatment as a potential explanation. Design Population-based retrospective cohort study using linked cancer registry and administrative data at ICES. Setting The universal healthcare system in Ontario, Canada. Participants Colorectal cancer (CRC) patients diagnosed between April 1st, 2007 and December 31st, 2012. SPI history (schizophrenia, schizoaffective disorders, other psychotic disorders, bipolar disorders or major depressive disorders) was determined using hospitalization, emergency department, and psychiatrist visit data and categorized as 'no history of mental illness, 'outpatient SPI history', and 'inpatient SPI history'. Main outcome measures Cancer-specific survival, non-receipt of surgical resection, and non-receipt of adjuvant chemotherapy or radiation. Results 24,507 CRC patients were included; 482 (2.0%) had an outpatient SPI history and 258 (1.0%) had an inpatient SPI history. Individuals with an SPI history had significantly lower survival rates and were significantly less likely to receive guideline recommended treatment than CRC patients with no history of mental illness. The adjusted HR for cancer-specific death was 1.69 times higher for individuals with an inpatient SPI (95% CI 1.36-2.09) and 1.24 times higher for individuals with an outpatient SPI history (95% CI 1.04-1.48). Stage II and III CRC patients with an inpatient SPI history were 2.15 times less likely (95% CI 1.07-4.33) to receive potentially curative surgical resection and 2.07 times less likely (95% CI 1.72-2.50) to receive adjuvant radiation or chemotherapy. These findings were consistent across multiple sensitivity analyses. Conclusions Individuals with an SPI history experience inequalities in colorectal cancer care and survival within a universal healthcare system. Increasing advocacy and the availability of resources to support individuals with an SPI within the cancer system are warranted to reduce the potential for unnecessary harm.