Ornithine decarboxylase as a marker for colorectal polyps and cancer.

There is as yet no specific chromosomal abnormality or gene marker identified for colorectal polyps and cancer. Thus available markers include only phenotypic markers. Tumor markers that have been studied include tetraploidy and increased colonic mucosal proliferation; and these markers have identified those patients that are at high risk for colon cancer. The current "gold standard" of colorectal cancer markers is the carcinoembryonic antigen (CEA). CEA is best used as a monitor of disease and recurrence, and not as a screening or diagnostic test. Newer carbohydrate markers include CA 19-9, incompatible A and B antigens, and T and Lewis antigens. These markers have not shown increased specificity or sensitivity compared to CEA. An interesting recently described marker is ornithine decarboxylase (ODC), which serves as a simple overall index of colonic mucosal proliferation. Ornithine decarboxylase levels have shown correlation with the progression from normal mucosa to adenoma and carcinoma, especially in hereditary polyposis syndromes. This enzyme may also serve as a potential therapeutic target. Many markers have been found useless in further clinical trials. Ornithine decarboxylase needs to be studied in greater detail to determine its sensitivity and specificity, in patients with hereditary colonic neoplasia and in patients without genetic syndromes.