Based on a "field-effect" theory in colon
carcinogenesis, and the expression of the
disaccharide tumor marker D galactose-beta-[1-->3]-
N-acetyl-D-galactosamine (
Gal-GalNAc) in the rectal mucus of patients with
cancer and precancer of the colon, Shamsuddin developed a simple, accurate, inexpensive, easy to perform and rapid (< or = 15 min) screening test for
colonic cancer and precancerous lesions. In this study we examined 137 rectal mucus samples of randomly selected patients with colorectal
malignancy or other colorectal diseases to confirm the sensitivity and specificity of this test in Croatia. Additionally, to test the validity of the "field-effect" theory, that the mucosa away from the obvious
cancer will show abnormalities as a result of the generalized effect of the
carcinogen throughout the entire field of the target tissue, we also monitored a subset of 53 patients post-operatively. Individuals free of colonic or any other
malignancies served as control (n = 31). The rectal
mucin was smeared on membrane filter and developed by a sequential reaction of
galactose oxidase (GO) and
Schiff's reagent. The test results were correlated to the findings from colonoscopy/surgery and histopathology. The sensitivity of the test was shown to be 100% and the specificity was 96.8% (p < 0.001). Interestingly, the test was positive in 60% (32 of 53) of the samples collected from patients after
tumor resection, showing the persistence of the biochemical changes even though malignant
tumors were removed, hence supporting the field-effect phenomenon of carcinogenic stimuli. Five patients out of these 32 (16%) postoperative cases with positive GO test had a
tumor recurrence within a year (0.05 < p < 0.10), suggesting that a persistently positive GO test in this population may serve as a predictor of
tumor recurrence. We conclude that
Gal-GalNAc is an early and intermediate
biomarker, suitable not only for the detection of
malignancy in its inception, but also for monitoring of people at high risk for
cancer, and the efficacy of the
cancer therapy as well as
secondary prevention by this technology.