The disease natural history of colorectal neoplasm is controversial and rarely quantified. It involves 2 opposing theories, the adenoma-carcinoma sequence and the de novo carcinoma theory.
In this study, researchers from Taiwan estimated the dwelling times of adenoma-carcinoma sequence by adenoma size and histological type. They also evaluated de novo carcinoma.
They performed a case-cohort study to estimate parameters associated with the 2 opposing theories.
The team studied patients from a cohort of 13,908 subjects, which included including 10,496 normal subjects, 2652 polyps, and 760 colorectal cancers.
| Patients with adenoma >1cm have a 4.3-fold risk of malignant transformation.|
|British Journal of Cancer|
All the 2652 polyps were linked to national cancer registry to ascertain 25 invasive carcinomas after polypectomy.
From this they randomly selected 305 patients with polyps, 116 with colorectal cancer, and 305 controls. All had undergone their first colonoscopy between 1979 and 1998.
The team found, using a five-state model associated with adenoma size, that dwelling times for small and large adenoma (>1 cm) were 7.8 and 5.3 years, respectively. When de novo carcinoma was taken into account, dwelling times were 17.5 and 15.9 years, respectively.
The researchers made similar observations for a model associated with histological type.
They estimated the proportion of de novo carcinoma as 31.9% from the adenoma size model, 27.8% from histological type model.
When compared to size <5mm, patients with adenoma size between 6 and 10mm have a 2.2-fold risk of malignant transformation. Patients with adenoma >1cm have a 4.3-fold risk. The team found that the histological type model predicted similar risks.
The research team estimated that the efficacy of colonoscopy in reducing CRC is 73%. This increased to 88% when the team used the model which considered de novo carcinoma.
In addition, the efficacy of diminutive adenoma and small adenoma increases with follow-up years, whereas the efficacy of large adenoma decreases with follow-up years.
Dr Chen's team concluded, "About 30% of cancers arising from de novo sequence are demonstrated".
"This finding, together with the adenoma-carcinoma sequence…is important for the estimation of dwelling times, the efficacy of colonoscopy, and the surveillance of polyp after polypectomy".