Objective: To assess the risk of colorectal cancer (CRC) in first degree relatives (parents and full siblings) of patients with precursor lesions (polyps) for CRC.
Design: Case-control study.
Setting: Linkage to the multi-generation register and gastrointestinal ESPRESSO (Epidemiology Strengthened by histoPathology Reports in Sweden) histopathology cohort in Sweden.
Participants: 68 060 patients with CRC and 333 753 matched controls.
Main outcome measures: Multivariable adjusted odds ratios of CRC according to the number of first degree relatives with a colorectal polyp and the histology of polyps and age at diagnosis in first degree relatives. Subgroup analysis was also performed according to age at CRC diagnosis and evaluated the joint association of family history of colorectal polyps and family history of CRC.
Results: After adjusting for family history of CRC and other covariates, having a first degree relative with a colorectal polyp (8.4% (5742/68 060) in cases and 5.7% (18 860/333 753) in controls) was associated with a higher risk of CRC (odds ratio 1.40, 95% confidence interval 1.35 to 1.45). The odds ratios ranged from 1.23 for those with hyperplastic polyps to 1.44 for those with tubulovillous adenomas. To better put this risk in perspective, the age specific absolute risk of colon and rectal cancers was estimated according to family history of polyps based on the 2018 national CRC incidence in Sweden. For example, the absolute risk of colon cancer in individuals aged 60-64 years with and without a family history of colorectal polyp was, respectively, 94.3 and 67.9 per 100 000 for men and 89.1 and 64.1 per 100 000 for women. The association between family history of polyps and CRC risk was strengthened by the increasing number of first degree relatives with polyps (≥2 first degree relatives: 1.70, 1.52 to 1.90, P<0.001 for trend) and decreasing age at polyp diagnosis (<50 years: 1.77, 1.57 to 1.99, P<0.001 for trend). A particularly strong association was found for early onset CRC diagnosed before age 50 years (≥2 first degree relatives: 3.34, 2.05 to 5.43, P=0.002 for heterogeneity by age of CRC diagnosis). In the joint analysis, the odds ratio of CRC for individuals with two or more first degree relatives with polyps but no CRC was 1.79 (1.52 to 2.10), with one first degree relative with CRC but no polyps was 1.70 (1.65 to 1.76), and with two or more first degree relatives with both polyps and CRC was 5.00 (3.77 to 6.63) (P<0.001 for interaction).
Conclusions: After adjusting for family history of CRC, the siblings and children of patients with colorectal polyps are still at higher risk of CRC, particularly early onset CRC. Early screening for CRC might be considered for first degree relatives of patients with polyps.
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