The risk and survival outcome of subsequent primary colorectal cancer after the first primary colorectal cancer: Cases from 1973 to 2012

Background: Among colorectal cancer (CRC) survivors, how the prior tumor location affects the risk of subsequent primary colorectal cancer (SPCRC) and the outcome of those suffering from SPCRC remain unknown. Methods: CRC cases diagnosed from 1973 to 2012 were screened for SPCRC development using the Surveillance, Epidemiology, and End Results database. The relative risk of SPCRC was estimated using the standardized incidence ratio. Survivals were analyzed using the Kaplan-Meier and Cox regression model. Results: The overall risk of SPCRC increased by 27% in CRC survivors compared to that of the general population. The risk increased in patients with both prior right colon cancer (RCC) and left colon cancer (LCC), and was concentrated in the first 5 years after the prior diagnosis, and among young patients. Among the 6701 SPCRC patients identified, patients with prior RCC were more likely to be elderly, female, and with more low or undifferentiated disease than those with prior LCC or rectal cancer (ReC). The overall survivals differed by both prior tumor location (P < 0.0001) and age (P < 0.0001), and the difference by tumor location remained significant when adjusted or stratified by any other potential prognostic factor except age. The cancer specific survivals differed by age (P < 0.0001) rather than by prior tumor location (P = 0.455). Conclusions: The overall risk of SPCRC increased among patients with both prior RCC and LCC, but not among those with ReC. The different survival outcomes in CRC survivors suffering from SPCRC were largely explained by the patient age but not by the prior tumor location.