Kavitha P Raj1, Thomas H Taylor2, Charlie Wray3, Michael J Stamos4, Jason A Zell5
1Chao Family Comprehensive Cancer Center, Division of Hematology/Oncology, Department of Medicine, School of Medicine, University of California Irvine, Irvine CA, USA.
2Genetic Epidemiology Research Institute, Department of Epidemiology, School of Medicine, University of California Irvine, Irvine CA, USA.
3College of Osteopathic Medicine of the Pacific, Western University of Health Sciences, Pomona, CA, USA
4Division of Colon and Rectal Surgery, Department of Surgery, School of Medicine, University of California Irvine, Irvine CA, USA.
5Chao Family Comprehensive Cancer Center, Division of Hematology/Oncology, Department of Medicine; Genetic Epidemiology Research Institute, Department of Epidemiology, School of Medicine, University of California Irvine, Irvine CA, USA.
Background: Patients with history of colorectal cancer (CRC) are at increased risk for developing a second primary colorectal cancer (SPCRC) as compared to the general population. However, the degree of risk is uncertain. Here, we attempt to quantify the risk, using data from the large population-based California Cancer Registry (CCR). Materials and Methods: We analyzed the CCR data for cases with surgically-treated colon and rectal cancer diagnosed during the period 1990-2005 and followed through up to January 2008. We excluded those patients diagnosed with metastatic disease and those in whom SPCRC was diagnosed within 6 months of the diagnosis of the primary CRC. Standardized incidence ratios (SIR) with 95% confidence intervals (CI) were calculated to evaluate risk as compared to the underlying population after taking into account age, sex, ethnicity, and time at risk. Results: The study cohort consisted of 69809 cases with colon cancer and 34448 with rectal cancer. Among these patients there were 1443 cases of SPCRCs. The SIR for developing SPCRC was higher in colon cancer survivors (SIR=1.4; 95% CI: 1.3 to 1.5) as compared to the underlying population. The incidence of SPCRC was also higher in females (SIR=1.5; 95% CI: 1.3 to 1.6) and Hispanics (SIR=2.0; 95% CI: 1.7 to 2.4) with primary colon cancer. The SIR for developing an SPCRC was higher only among those whose initial tumor was located in the descending colon (SIR=1.6; 95% CI: 1.3 to 2.0) and proximal colon (SIR=1.4; 95% CI: 1.3 to 1.6). Conclusions: Our results confirm that CRC patients, especially females and Hispanics, are at a higher risk of developing SPCRC than the general population. Differential SPCRC risk by colorectal tumor subsite is dependent on gender and ethnicity, underscoring the heterogeneous nature of CRC.
Keywords: Cancer registry, colon cancer, colorectal cancer, rectal cancer, second primary cancer