We read with interest the article by Matsumoto et al reporting their observations on the presence of serrated adenomas in familial adenomatous polyposis (FAP) patients in relation to germline APC mutations (Gut 2002;50:402–4). Their small colonoscopic study identified three FAP patients with serrated adenomas; all had less than 100 polyps and they concluded that serrated adenomas may be characteristic of attenuated FAP.
It is our practice to perform prophylactic colectomy with ileorectal anastomosis or ileoanal pouch formation in patients with FAP in the second or third decade or as soon as possible after a new diagnosis is established. An expert histopathologist performs a meticulous examination of the colectomy specimen, including a formal polyp count. Thereafter any rectal remnant is surveyed six monthly by flexible sigmoidoscopy with endoscopic snare polypectomy and argon plasma coagulation of suspicious lesions.
A simple search of the St Mark’s polyposis registry has revealed eight patients in whom serrated adenomas have been identified. In five patients the lesion was present in the colectomy specimen, in two the diagnosis was made on flexible endoscopic surveillance, and in one case a serrated adenoma was present in a polyp surgically excised from the rectum (table 1▶).
Table 1 .
Patient characteristics of eight patients in whom serrated adenomas were identified in St Mark’s polyposis registry
| Patient No (sex) | Age at colectomy (y) | Preoperative endoscopy | Colectomy specimen polyp count | Site and size of serrated adenoma | APC mutation analysis |
|---|---|---|---|---|---|
| 1 Male | 29 | Not available | 3550 | Sigmoid colon 1.2 cm (colectomy) | Ex 15 4175 c >g |
| 2 Female | 36 | Classical FAP | 1230 | Descending colon 0.5 cm (colectomy | Under investigation |
| 3 Male | 19 | Low polyp count | Not available | Rectum 0.5 cm (colectomy) | Unsuccessful |
| 4 Female | 39 | Classical FAP | 900 | Rectal polyp (surgical excision) | Unsuccessful |
| 5 Female | 17 | Classical FAP | 648 | Descending colon (colectomy) | Ex 15 2367-2368 deletion |
| 6 Male | 19 | Low polyp count | 868 | Rectal biopsy | Unsuccessful |
| 7 Male | 19 | Classical FAP | Hundreds | Rectal biopsy | Ex 15 3254-3257 del |
| 8 Female | 14 | Not available | 1425 | Colectomy specimen | Unsuccessful |
FAP, familial adenomatous polyposis.
As in Matsumoto’s study, in the majority of the St Mark’s cases the serrated adenoma was located distally either in the sigmoid colon or rectum. However, in our patients serrated adenomas were not restricted to those with the attenuated phenotype. Seven of the St Mark’s patients with serrated adenomas have classical FAP with more than 100 colonic polyps in the colectomy specimen. (In one of these patients preoperative colonoscopy reported a low polyp count.) The genetic mutations have been identified in three of our patients and all were in exon 15, rather than more proximally.
Serrated adenomas may be a feature in FAP but they are not characteristic of the attenuated phenotype. Colonoscopy alone may underestimate the number of colorectal polyps, especially in difficult cases. We believe that dye spray colonoscopy by an experienced endoscopist and careful examination of colectomy specimens are necessary to completely characterise the FAP phenotype.
The clinical significance of the presence of serrated adenomas in FAP patients has yet to be determined. Further studies in this interesting area are required.