The survival of the prostate cancer patients with secondary colorectal cancer: a study based on a SEER database from southern China.

To evaluate the prognosis of prostate cancer patients with secondary colorectal cancer.The study included men with prostate cancer who developed colorectal cancer after radical prostatectomy in the Surveillance, Epidemiology, and Outcomes (SEER) database. After adjusting the age at first diagnosis, the prostate-specific antigen (PSA) level and Gleason score, the influence of the occurrence of secondary colorectal cancer on the prognosis of patients was evaluated.A total of 66,955 patients were included in the present study. The median follow-up was 12 years. There were 537 patients with the incidence of the secondary colorectal cancer. The results of the three survival analysis methods all showed that the secondary colorectal cancer greatly increased the mortality risk of prostate cancer patients. Cox analysis results showed the hazard ratio (HR) is 3.79 (3.21-4.47), the Cox model with time-dependent covariates was introduced, and the result was 6.15 (5.19-7.31). When the Landmark time point is set to 5 years, the HR is 4.99 (3.85-6.47).This study provides an important theoretical basis for evaluating the effect of secondary colorectal cancer on the prognosis of prostate cancer patients.