Secondary Primary Prostate Cancer after Colorectal Cancer: A Nationwide Population-based Cohort Study in Korea.

Background: Colorectal cancer (CRC) and prostate cancer frequently occur in developed countries. There are several reports on the association between CRC and prostate cancer; however, the conclusions are inconsistent to investigate the association of the development of secondary primary prostate cancer among patients with prior primary CRC using a nationwide population-based dataset.

Methods: Patients registered in the Republic of Korea National Health Insurance System database who were diagnosed with CRC between 2007 and 2012 were followed-up until the end of 2015, and we investigated the new diagnosis secondary primary prostate cancer. We compared the incidence of prostate cancer in age-matched controls using the Cox proportional hazards models.

Results: We analyzed a total of 85,455 first primary CRC survivors. During the follow-up period of 494,222 person-years, 2,005 patients (2.30%) developed secondary primary prostate cancer (incidence rate 4.06/1,000 person-years). The median duration of follow-up was 5.78 years. Compared with the general population, CRC patients had a significantly increased risk of secondary primary prostate cancer (HR = 2.30, 95% CI = 2.18-2.43; P < 0.001). Multivariate analysis (including age, sex, body mass index, hypertension, diabetes mellitus, dyslipidemia, and income) showed that age < 55 years (HR = 20.74, 95% CI = 11.81-36.41; P < 0.001) is a significant independent predictor of secondary primary prostate cancer development.

Conclusions: Men diagnosed with colorectal cancer are at an increased risk of secondary primary prostate cancer, particularly those aged < 55 years. The data suggests that colorectal cancer patients aged < 55 years require regular screening for prostate cancer.