Risk of colorectal cancer after the diagnosis of prostate cancer: A population-based study.

BACKGROUND

A rigorous assessment of the risk of colorectal cancer (CRC) among prostate cancer (PC) survivors that controls for important confounding factors and competing risks is necessary to determine the risk of CRC in this population and to inform screening guidelines.

METHODS

With data from Manitoba, Canada, subjects diagnosed with PC as their first cancer between 1987 and 2009 were age-matched with up to 5 men with no history of invasive cancer on the PC diagnosis date. Subjects were followed to the date of diagnosis of CRC or another cancer, death, emigration, or the study endpoint (December 31, 2009). Competing risk proportional hazards models were used to compare the CRC incidence between those with PC and those without PC with the following model covariates: history of lower gastrointestinal endoscopy, frequency of health care visits, diabetes, and socioeconomic status. Mutually exclusive competing outcomes included CRC, another primary cancer, and death.

RESULTS

For a total of 559,081 person-years, 14,164 men with PC and 69,051 men without PC were followed. Men diagnosed with PC had an increased risk of a subsequent diagnosis of CRC (all CRC: hazard ratio [HR], 1.14; 95% confidence interval [CI], 1.02-1.27; rectal cancer: HR, 1.36; 95% CI, 1.09-1.71). The treatment of PC with radiation was associated with an increased risk for rectal cancer (HR, 2.06; 95% CI, 1.42-2.99) in comparison with PC cases not treated with radiation.

CONCLUSIONS

The risk of CRC is increased after a diagnosis of PC and is highest for rectal cancer among those treated with radiation. CRC screening should be considered soon after the diagnosis of PC, especially for men planning for radiotherapy.