While I was studying the update on colorectal cancer published last July in Surgical Clinics, I found some interesting ideas about colorectal cancer screening and polyp management.
The main idea was the uncertain about natural history of the untreated polyp, since in the modern era most polyps are endoscopically removed to prevent growth and to ensure accurate diagnosis. Nowadays it would be unethical to let a polyp growth and study how long it would take till it gets malignant. In that setting, a Mayo Clinic study published in 1987 and referenced in the "difficult colorectal polyp" chapter, got my attention.
In 1987, Steven J. Stryker from The Mayo Clinic presented a retrospective review of 226 who were diagnosed with colonic polyps between January 1965 and December 1970, and were left untreated and followed by single-contrast fluoroscopic barium enema. This 6yr period was just before the introduction of colonoscopy in that institution. There were criteria for polyp inclusion in the follow-up study:
radiographic demonstration of a polyp ≥10mm
polyp demonstrated in at least two consecutive barium enema
radiological surveillance period beyond one year
no polyposis coli or inflammatory bowel disease
One index polyp was selected for each patient (some patients had several polyps), growth was defined as an increase >25% in diameter, and a 12 mo interval was used between barium enema examinations. Maximum polyp follow-up was 229 mo (19yr) with a mean of 68mo (6yr). I would like to enhance that 12% of polyps were ≥20mm.
During the surveillance period polyp enlargement was noticed in 87 polyps (37%). A total of 107 (47%) polyps were excised mostly because of growth. An invasive adenocarcinoma was found at the site of index polyp in 21 patients (20%) at a mean follow-up of 108mo (9yr). Additionally, invasive adenocarcinoma at remote site from index polyp was diagnosed in 11 patients. From these data the authors presented a cumulative risk of malignancy at the site of index polyp of 2,5% at 5yr, 8% at 10yr, and 24% at 20yr. They also presented a cumulative risk of diagnosing a cancer at any site at 5yr, 10yr and 20 yr of 4%, 14% and 35%, respectively.
The authors concluded (in 1987) that "this study supports the already prevalent opinion about excision of all colonic polyps ≥10mm". They also stated that even if only a few polyps progress to cancer, "the risk of this occurrence far outweighs the risk of treatment" with colonoscopic polypectomy.
I found interesting and important that these data presented in 1987 by the Mayo Clinic group about the natural history of colonic polyp are still the base for some statements and indications in the present day...
In Surgical Clinics update on colorectal cancer, screening is indicated till the age of 75 years old since after this mark the benefit of screening declines. Additionally screening is not indicated for individuals more than 86yo, and between 76 and 85 years old the indication must be individualised. Benefits must be weighed with the risks of colonoscopy. It is also state in Surgical Clinics that "this slow rate of growth must be taken into account when recommending therapy for elderly patients or patients with significant life limiting comorbidities".
So, the indication is based on the natural history of the colonic polyp since only 24% of them will arbor a cancer after 20yrs. How many individuals with 86 years old will live for 20yrs more?... Also, if you are diagnosed with a colonic polyp at the age of 76yo you will have a 24% chance of arboring a cancer in the same polyp by the age of 96 years old... Will you have that polyp (≥10mm) excised? Will the benefits overweight the risk of bleeding and perforation of colonoscopy? Will the risk of complications from mechanical bowel preparation be neglectable in this situation? You must remember that these are benign polyps with potential for malignancy, not a diagnosed cancer.
It was interesting to read in the study from Stryker et al. that in 1987 there was still debate about the relation of colonic adenoma with the cancer origin. In the present day this correlation is well known and presented as the adenoma-carcinoma sequence, and because of that it won't be possible to perform another similar study in the future. That is why I wanted to present you with this potential historical paper.
Learn the past to understand the present and prepare the future.
Link to PubMed:
Dr. Carlos Eduardo Costa Almeida
General Surgeon