Prostate Cancer Survivors Have Elevated CRC Risk

A large cohort study showed that the risk of colorectal cancer (CRC) is increased following a diagnosis of prostate cancer (PC). This suggests CRC screening should be considered following a PC diagnosis, especially among those undergoing radiotherapy.

“Second primary malignancies are important causes of morbidity and mortality in cancer survivors and can be due to shared etiologic (environmental and genetic) factors or prior cancer treatment,” wrote study authors led by Harminder Singh, MD, MPH, of the University of Manitoba in Winnipeg, Canada. Previous studies on CRC risk in PC patients have yielded mixed results, but suffered from a variety of limitations.

“If men with a history of PC are truly at higher than average risk of developing CRC, then the standard CRC screening paradigm may need to be altered for them,” the authors wrote. They conducted a historical cohort study based on data collected within the province of Manitoba, covering a total of 14,164 men with PC and 69,051 controls without PC, for a total of 559,081 person-years. The results were published online ahead of print in Cancer.

Over the course of the follow-up period, 2.8% of the PC survivors were diagnosed with CRC, compared with 2.6% of the non-PC cohort. The hazard ratio for PC survivors being diagnosed with CRC was 1.14 (95% CI, 1.02–1.27; P = .021). The risk was elevated throughout the follow-up period, but it was “marginally not significant” between 31 days and 1 year after PC diagnosis, and beyond 5 years. The highest risk was seen from diagnosis of PC to 30 days, with an HR of 3.04 (95% CI, 1.42–6.51; P = .004).

The elevated CRC risk was driven by an elevated risk specifically for cancer of the rectum, with an HR of 1.36 (95% CI, 1.09–1.71; P = .008). No other subsite showed any elevated risk for PC patients.

The use of radiation therapy for PC was also associated with an elevated risk of CRC. For rectal/rectosigmoid CRC, the HR was 2.06 compared with men with PC not treated with radiation (95% CI, 1.42–2.99; P < .001). This risk increased over time; after 10 years from radiation therapy for PC, the HR was 4.91 (95% CI, 1.81–13.31; P = .002). For nonrectal/rectosigmoid CRC, the HR for the full follow-up period was 1.46 (95% CI, 1.07–1.99; P = .017).

“Screening for CRC and its precursor lesions should be considered soon after the diagnosis of PC, especially in men to be treated with radiation therapy,” the authors concluded.