Guidelines for colonoscopic screening in acromegaly are inconsistent with those for other high risk groups

We welcome the joint work of the British Society of Gastroenterology and the Association of Coloproctology of Great Britain and Ireland in commissioning guidelines for colorectal cancer screening in high risk groups (Gut 2002;51(suppl 5):V13–14). In the absence of direct evidence from randomised trials for most of the groups, the various authors have balanced a wealth of recent genetic and epidemiological evidence estimating an individual’s levels of elevated risk against the risks associated with screening. The end result is the recognition that within the label “high risk” there is a spectrum of risks such that colonoscopic screening and surveillance must be tailored accordingly. This avoids the ineffective, costly, and potentially harmful “blanket-type” approach, which formerly prevailed.

However, within the guideline series, there is one exception—screening and surveillance in patients with acromegaly. We and other researchers^1–3 have repeatedly stated that the studies undertaken by the authors of these guidelines have overestimated the risk of colorectal cancer in this patient group. They report a 13–14-fold increase in risk based on colorectal cancer detection rates among acromegalics undergoing colonoscopy at Barts compared with cancer rates from published series of colonoscopic screening in non-acromegalic subjects (see table 3 in Jenkins and Besser⁴). All of these “control” studies are in mixed race US populations and lack data to permit age-sex comparisons. This simply does not rank as a well designed controlled study and the recommendations should not receive grade B status.

In the same manner as relative risks for those with relatives with colorectal cancer are estimated from population based data (summarised in Dunlop⁵), we have argued for a similar approach for patients with acromegaly.¹ Based on three population based studies, we calculated (by fixed effects meta-analysis) a relative risk of 2.0 (95% confidence intervals 1.4–2.9) for colon and rectal cancer combined in acromegalics.^1,2 Considered in terms of absolute risk, with an approximate 2% cumulative risk of colorectal cancer by age 70 years in the general UK population, the estimated risk in acromegalics would be 4%. Notably, the incidence in the Barts series is 4.5% (10 of 222)—not a quarter if the estimate of a 13-fold increase was applied. Acromegalic patients thus have a modest increase in colorectal cancer risk, not a high risk. In first degrees relatives with a strong family history (a high risk group), Dunlop⁵ recommends early colonoscopic screening and then wait until 55 years for repeat colonoscopy if initial screening is clear (the majority). How can Jenkins and Fairclough justify early screening and colonoscopy five yearly thereafter in all of their acromegalics?

Atkin and Saunders⁶ have demonstrated that colonoscopic surveillance following initial screening in the non-acromegalic population is determined primarily by clinicopathological findings. These basic guidelines must also be applied to the acromegalic patient population. Jenkins and Fairclough have stated that elevated serum IGF-I levels may predict for recurrent adenomas in acromegalic patients and “should be offered screening at three year intervals”. This is based on data from only eight acromegalic patients with recurrent adenomas⁷ and should not replace other well recognised predictors of recurrence.

Looked at in the context of (other high risk) groups, the guidelines for colorectal cancer screening in patients with acromegaly are inconsistent. The aggressive approach to colonoscopic screening recommended by Jenkins and Fairclough should be seriously questioned.