MONOSOMY OF CHROMOSOME-18 DETECTED BY FLUORESCENCE IN-SITU HYBRIDIZATION IN COLORECTAL TUMORS

Background. At least two different evolutional pathways of colorectal cancer, namely the adenoma-carcinoma sequence and de novo carcinogenes is, have been indicated. However, whether there is a difference betwee n them in affected chromosomes and genes has not yet been elucidated. Chromosomal examination is expected to provide a clue to an answer to this question. In this study, the relation of aberrations in chromosom e 18 to type of colorectal cancer was examined. Methods. Numeric aberr ations in chromosome 18 were investigated in 71 colorectal tumors by m eans of fluorescence in situ hybridization, using an alphoid satellite DNA probe specific for the pericentromeric region on chromosome 18. R esults. The loss of one chromosome 18 was found in 33% (6 of 18) of pa tients with early cancer, excluding those with cancer in an adenoma. T he loss was frequent in early colorectal carcinomas without foci of ad enoma (four of six patients, 67%), whereas monosomy 18 was not signifi cant in those with foci of adenoma except for patients with a heredita ry background. Specimens exhibiting monosomy 18 were macroscopically c lassified as hat lesions, but the converse was not true. No adenoma sh owed monosomy 18. It was encountered in 44% of nine cancers with invas ion to the muscularis propria. However, no significant subpopulation o f monosomy 18 was present in cancers penetrating through the serosa or adventitia in which polysomic populations were often identified alter natively. Furthermore, tetrasomy for this chromosome was exclusive in these advanced cancers. Conclusions. The loss of chromosome 18 is clos ely related to colorectal cancers without foci of adenoma.