Results from the first study to comprehensively characterise colorectal cancer incidence and mortality in relation to different histological subtypes of polyps in a largely screening-naive population are published on 16 March 2020 in The Lancet Gastroenterology & Hepatology. Compared with matched reference individuals, incidence of colorectal cancer was higher in patients with any polyp subtype. The risk increased with advanced histology of the index polyp. For colorectal cancer mortality, an increased risk was found in individuals with sessile serrated polyps, tubulovillous adenomas, and villous adenomas, but not in those with hyperplastic polyps or tubular adenomas. Therefore, the patients with sessile serrated polyps, tubulovillous adenomas, and villous adenomas might benefit from colonoscopy surveillance.
Endoscopic screening reduces colorectal cancer incidence and mortality by detection and removal of precursor lesions. Although the conventional adenoma–carcinoma sequence has been well described and accounts for the majority of cases of colorectal cancer, an alternative pathway exists for another 20–30% of cases in which sessile serrated polyps represent the major precursor lesions.
Long-term colorectal cancer incidence and mortality after colorectal polyp removal remains unclear which prompted the researchers from Sweden to assess colorectal cancer incidence and mortality in individuals with removal of different histological subtypes of polyps relative to the general population.
They did a matched cohort study through prospective record linkage in patients aged at least 18 years with a first diagnosis of colorectal polyps in the ESPRESSO (Epidemiology Strengthened by histoPathology Reports in Sweden) cohort (1993–2016). For each polyp case, they identified up to five matched reference individuals from the Total Population Register on the basis of birth year, age, sex, calendar year of biopsy, and county of residence. Colorectal cancer cases were identified from the Swedish Cancer Registry, and cause-of-death data were retrieved from the Cause of Death Register.
In total, 178377 patients with colorectal polyps and 864831 matched reference individuals from the general population were included in the study. The mean age of patients at polyp diagnosis was 58.6 years for hyperplastic polyps, 59.7 years for sessile serrated polyps, 63.9 years for tubular adenomas, 67.1 years for tubulovillous adenomas, and 68.9 years for villous adenomas.
During a median of 6.6 years of follow-up, the study team documented 4278 incident colorectal cancers and 1269 colorectal cancer-related deaths in patients with a polyp, and 14350 incident colorectal cancers and 5242 colorectal cancer deaths in general reference individuals.
The 10-year cumulative incidence of colorectal cancer was 1.6% (95% confidence interval [CI] 1.5–1.7) for hyperplastic polyps, 2.5% (1.9–3.3) for sessile serrated polyps, 2.7% (2.5–2.9) for tubular adenomas, 5.1% (4.8–5.4) for tubulovillous adenomas, and 8.6% (7.4–10.1) for villous adenomas compared with 2.1% (2.0–2.1) in reference individuals.
Compared with reference individuals, patients with any polyps had an increased risk of colorectal cancer, with multivariable hazard ratio (HR) of 1.11 (95% CI 1.02–1.22) for hyperplastic polyps, 1.77 (1.34–2.34) for sessile serrated polyps, 1.41 (1.30–1.52) for tubular adenomas, 2.56 (2.36–2.78) for tubulovillous adenomas, and 3.82 (3.07–4.76) for villous adenomas (p < 0.05 for all polyp subtypes).
There was a higher proportion of incident proximal colon cancer in patients with serrated (hyperplastic and sessile) polyps (52–57%) than in those with conventional (tubular, tubulovillous, and villous) adenomas (30–46%).
For colorectal cancer mortality, a positive association was found for sessile serrated polyps (HR 1.74, 95% CI 1.08–2.79), tubulovillous adenomas (1.95, 1.69–2.24), and villous adenomas (3.45, 2.40–4.95), but not for hyperplastic polyps (0.90, 0.76–1.06) or tubular adenomas (0.97, 0.84–1.12).
The authors concluded that the patients with any polyp subtype had a higher risk of colorectal cancer incidence than the reference individuals in this largely screening-naive population. The risk elevation increased with advanced histology for both conventional adenomas and serrated polyps. In contrast, the risk of colorectal cancer mortality was increased only in patients with sessile serrated polyps, tubulovillous adenomas, or villous adenomas. The findings suggest that patients with these 3 types might benefit from colonoscopy surveillance. Further studies are needed to examine the impact of colonoscopy surveillance on prevention of colorectal cancer.
The study was supported by the US National Institutes of Health, American Cancer Society, American Gastroenterological Association, and Union for International Cancer Control.
Reference
Song M, Emilsson L, Bozorg SR, et al. Risk of colorectal cancer incidence and mortality after polypectomy: a Swedish record-linkage study. The Lancet Gastroenterology & Hepatology; Published online 16 March 2020.