Chromosome analysis of adenomatous polyps of the colon: possible existence of two differently evolving cytogenetic groups.

A chromosomal study of 42 colonic adenomatous polyps was performed using a technique of direct chromosome analysis derived from the prenatal procedure for diagnosing chromosomal alterations from chorionic villi sampling. Abnormal karyotypes were found in 22 cases. Trisomy 7, the most frequently found alteration, was found in 13 cases, followed by trisomy 13 (nine cases). Monosomy 18 was observed in two cases; in one of these, that of a polyp which had degenerated into an intra-mucosal adenocarcinoma, it was associated with 17p monosomy. Interestingly, these two types of alterations (trisomy 7 versus 18 and 17p monosomy) were not found together in the same lesion. This suggests that there could be two distinct chromosomal behaviors which might be related to the two cytogenetic groups described for colorectal adenocarcinoma. However, the respective frequencies of such cytogenetic groups varied inversely between adenomas and adenocarcinomas, thus suggesting that they evolve differently.