Peter S. Rabinovitch MD, PhD, Brian J. Reid MD, PhD, Rodger C. Haggitt MD, Douglas S Levine MD, Cyrus E Rubin MD. University of Washington, Seattle, WA, USA.

Less attention has been given to the study of flow cytometry in the management of patients at risk for future cancer than has been given to study of patients who already have cancer. We have studied DNA flow cytometry in two gastrointestinal diseases with an increased risk of development of cancer - Barrett's esophagus and chronic ulcerative colitis. Over 8000 biopsies from over 500 patients have been evaluated by flow cytometry. While intensive endoscopic surveillance can detect high grade dysplasia or early cancer at a curable stage, such surveillance can be impractical. Flow cytometry helps to identify the subset of patients in whom close endoscopic surveillance is most indicated for the detection of early, curable disease. Conversely, the larger subset of patients who are at lower risk can be subjected to less frequent and less costly surveillance.

In Barrett's esophagus the finding of aneuploidy or elevated G2/tetraploid fractions is increasingly frequent with more advanced histologic category (metaplasia -> indefinite/low grade dysplasia -> high-grade dysplasia -> cancer). The finding of elevated G2/tetraploid fractions appears to be an earlier event than aneuploidy, and is associated with a high risk of progression to aneuploidy, with a mean interval for progression of 17 months. Patients who have progressed to high-grade dysplasia or cancer frequently have developed multiple aneuploid populations (mean of 6.5) within their esophagus. To determine the prognostic value of flow cytometry, we evaluated 62 patients with Barrett's esophagus prospectively (mean interval 34 mo.): 9/13 patients who had aneuploid or increased G2/tetraploid populations in their initial flow cytometry developed high-grade dysplasia or adenocarcinoma during follow-up; 0/49 patients without these abnormalities progressed. This result is highly significant (p<0.0001). Patients with flow cytometric abnormalities should be closely examined at frequent (6 mo.) intervals, whereas those who are without dysplasia or flow cytometric abnormalities can be examined less frequently (>2yrs.).

In chronic ulcerative colitis (UC), DNA aneuploidy is also found with increasing frequency with histologic stage: 0/20 patients with short duration/non-extensive disease; 1/33 with high risk (chronic or extensive) histologically negative UC; (6/13) high risk with indefinite histology; and 22/25 with frank dysplasia. As in Barrett's esophagus, multiple aneuploid populations (up to 15) are frequently found in patients who have dysplasia or cancer. We have prospectively followed 25 high risk patients with histologically negative or indefinite UC: 6/6 with initial aneuploidy progressed whereas only 1/20 without initial aneuploidy progressed (p<.0001).

In ulcerative colitis, dysplasia or cancer can often be focal, and the target organ is large. By examining colectomy specimens in great detail (often more than 100 flow cytometric and 100 histologic samples per colon), we have concluded that 33 biopsies must be examined histologically and 20 biopsies examined by flow cytometry in order to achieve 90% confidence that dysplasia and aneuploidy, respectively, would be detected, if present. These large number of examinations are often impractical. We have found, however, that by pooling four biopsy specimens from a given segment of colon, the number of analyses required for flow cytometric surveillance can be reduced by 75% (from 20 to 5), with only slight loss of sensitivity. Pooling samples makes flow cytometry both a practical and affordable tool in identifying ulcerative colitis patients, some of whom may not yet have overt dysplasia, but who are at high risk for developing it. Perhaps most importantly, the large group of patients whose mucosal biopsy specimens are histologically negative for dysplasia and have a diploid DNA content appear to be at low risk of progressing to dysplasia; they can probably have their surveillance interval lengthened to 3 years, with a consequent savings in time and resources.