Second Primary Cancer Occurrence after Colorectal Cancer: A Systematic Review and Meta-Analysis

Abstract Background Colorectal cancer (CRC) is the third most frequent cancer diagnosis and the second leading cause of cancer-related death. There is evidence of an increased risk of developing a second primary colorectal cancer in CRC patients. Objective This systematic review and meta-analysis aims to provide a pooled relative risk of second primary cancer after colorectal cancer (SPCAC) in CRC patients based on available evidence. Data Sources: Medline (via PubMed), Web of Science, and Scopus databases were searched for English cohort studies that reported standard incidence ratio (SIR) of SPCAC up to 10 Aug 2020. Heterogeneity across included studies was determined using the I2 statistic. We used the random‑effect models for pooled Standard Incidence Ratio (SIR) and 95% confidence intervals (CIs). Study Selection : Studies included if they met the following criteria: original studies with cohort design in the English language; studies that investigated and reported the SIR of second primary cancer after colorectal, colon, and rectum cancer. Main Outcome Measures : The pooled SIR of SPCAC based on the primary site of cancer was measured. Results Through 30 extracted papers, 142429 confirmed SPCAC adult patients (more than 19 years old) were included in this meta-analysis. The SIR of SPCAC was 1.27 (95% CI 1.16–1.37) and was reported by 12 studies. The SIR of SPCAC for digestive, reproductive, and urinary organ’s involvement was 1.31 (95% CI 0.89–1.72), 1.45 (95% CI 0.99–1.90), and 1.27 (95% CI 1.10–1.45), respectively. Limitations : Unavailable confounding characteristics such as smoking, alcohol intake, physical activity, food, and lifestyle, may restrict the findings. Conclusions Colorectal cancer survivors (CCSs) are more vulnerable to SPCAC of the small intestine and endometrium. The result of this study might be helpful for both clinicians and policymakers. Further investigations on etiologic factors for prevention and early diagnosis of SPCAC are suggested.