LETTER
Which Colonic Adenomas Became Malignant?
Alfred I. Neugut and
Judith S. Jacobson
1 August 1993 | Volume 119 Issue 3 | Pages 250-252
TO THE EDITOR:
We agree with Koretz [1] that the evidence regarding the adenoma-carcinoma sequence is circumstantial, that malignant polyps may have a long latency period, that some colorectal cancer appears to arise de novo, and that the similarity in the distribution of adenomas and cancer may be caused by a field defect in the colorectal mucosa that gives rise to both.
However, other factors need to be considered as well. The prevalence of adenomas found at autopsy in different populations is highly correlated with cancer incidence (r = 0.67). The mean age for cancer is approximately 7 years older than that for adenomas [2], consistent with the adenoma-carcinoma sequence. In follow-up studies, patients who underwent polypectomy had a cumulative relative risk of at least 2.5 when compared with patients who did not have polyps [2]. Adenomas and cancer are also associated with similar dietary and other risk factors [2, 3]. Koretz cites but does not describe a study of 226 patients with untreated polyps 10 mm or greater in diameter, in which 10% of patients developed cancer at the same site and an additional 5% developed cancer at another site (mean follow-up, 9 years) [4].
These observations are circumstantial but persuasive. The adenoma-carcinoma sequence hypothesis may never be "proved," but until refuted it is the most parsimonious explanation for the above observations. The hypothesis does not imply that every adenoma removed is a human life saved. Similarly, fastening one's seatbelt does not save one's life most of the time.
If patients with adenomas have only twice the risk for cancer as controls and if not having the polyp removed only doubles that risk, screening and polypectomy would seem to be a reasonable prevention policy in a nation with a 7% lifetime risk for colorectal cancer.
1. Koretz RL. Malignant polyps: are they sheep in wolves' clothing? Ann Intern Med. 1993; 118:63-8.
2. Neugut AI, Jacobson JS, DeVivo I. The epidemiology of colorectal adenomatous polyps. Cancer Epidemiol Biomarkers Prev. 1993; 2: 159-76.
3. Neugut AI, Garbowski G, Lee WC, Murray T, Nieves JW, Forde KA, et al. Dietary risk factors for the incidence and recurrence of colorectal adenomatous polyps. Ann Intern Med. 1993; 118:91-5.
4. Stryker SJ, Wolff BG, Culp CE, Libbe SD, Ilstrup DM, MacCarty RL. Natural history of untreated colonic polyps. Gastroenterology. 1987; 93:1009-13.
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