The Risk of Second Primary Colorectal Adenocarcinomas Is Not Increased among Patients with Gastroenteropancreatic Neuroendocrine Neoplasms: A Nationwide Population-Based Study.

BACKGROUND:Second primary colorectal adenocarcinomas (SPCA) may occur with a higher frequency in patients with gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs). In a nationwide population-based study, we investigated the risk of SPCA in GEP-NEN patients and compared it to the general population. METHODS:Using the nationwide Danish registries, we identified 2,831 GEP-NEN patients (median age 63 years [IQR 50-73 years], 53% women) diagnosed in 1995-2010. We used Cox regression to compare the incidence of SPCA in GEP-NEN patients relative to a gender- and age-matched general population sample of 56,044 persons. RESULTS:We observed 20 SPCAs among the 2,831 GEP-NEN patients with a total time at risk of 14,003 years (incidence = 143 per 100,000 person-years) and 770 colorectal adenocarcinomas in the general population of 56,044 persons with a total time at risk of 466,801 years (incidence = 165 per 100,000 person-years). The hazard ratio (HR) of SPCA from GEP-NEN diagnosis to the end of follow-up was 1.22 (95% CI: 0.78-1.92) in GEP-NEN patients compared to the general population. This nonsignificant association was the result of a strong positive association in the first 6 months after diagnosis of GEP-NEN (HR = 9.43 [95% CI: 4.98-17.86]) followed by a negative association in the remainder of the follow-up period (HR = 0.50 [95% CI: 0.20-1.21]). CONCLUSION:In this population-based study, there was no increased risk of SPCA among GEP-NEN patients. The clinical workup in newly diagnosed GEP-NEN patients likely explains the positive short-term association followed by a negative association.