Influence factors of the survival in colorectal cancer patients with second primary malignancy after surgery: A SEER database analysis

The survival rate is significantly reduced in patients with colorectal cancer (CRC) who developing a second primary malignancy (SPM), and however, little has known about the factors that contribute to the mortality of SPMs among CRC survivors. This study aims to explore the influence factors in both the all-cause and cancer-specific mortality of patients with SPMs after CRC surgery. Data of adult CRC patients with SPMs were extracted from the Surveillance, Epidemiology, and End Results (SEER) database in this retrospective cohort study. The associations between potential influence factors and all-cause mortality and cancer-specific mortality were explored using univariate and multivariate Cox proportional hazards analyses. The evaluation indexes were hazard ratios (HRs), and 95% confidence intervals (CIs). We also drew pie charts to respectively reflect the distributions of SPMs sites and time interval in study population. A total of 1202 (56.14%) patients died for all-cause, and 464 (21.67%) died due to CRC. The results showed that after adjusting for covariates, age, sex, marital status, T stage of CRC, second primary cancer site, stage of SPMs, grade of SPMs, TNM stage of SPMs, and time interval were associated with all-cause mortality, while marital status, stage of CRC, T stage of CRC, chemotherapy, second primary cancer site, stage of SPMs, grade of SPMs, TNM stage of SPMs, and time interval were associated with cancer-specific mortality in patients with CRC. In addition, colon (23.5%) was the most common site of SPMs, followed by digestive system (19.0%), and the time interval between CRC and SPMs in most patients was over 5 years (28.4%). Our findings may assist clinicians to identify high-risk patients for SPMs after CRC surgery. Also, the postoperative long-term follow-up and close attention on the key systems where the SPMs may occur are of great necessary in patients with CRC.