Monosomy of chromosome 18 detected by fluorescence in situ hybridization in colorectal tumors.

At least two different evolutional pathways of colorectal cancer, namely the adenoma-carcinoma sequence and de novo carcinogenesis, have been indicated. However, whether there is a difference between 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 chromosome 18 to type of colorectal cancer was examined. Numeric aberrations in chromosome 18 were investigated in 71 colorectal tumors by means of fluorescence in situ hybridization, using an alphoid satellite DNA probe specific for the pericentromeric region on chromosome 18. The loss of one chromosome 18 was found in 33% (6 of 18) of patients with early cancer, excluding those with cancer in an adenoma. The loss was frequent in early colorectal carcinomas without foci of adenoma (four of six patients, 67%), whereas monosomy 18 was not significant in those with foci of adenoma except for patients with a hereditary background. Specimens exhibiting monosomy 18 were macroscopically classified as flat lesions, but the converse was not true. No adenoma showed monosomy 18. It was encountered in 44% of nine cancers with invasion to the muscularis propria. However, no significant subpopulation of monosomy 18 was present in cancers penetrating through the serosa or adventitia in which polysomic populations were often identified alternatively. Furthermore, tetrasomy for this chromosome was exclusive in these advanced cancers. The loss of chromosome 18 is closely related to colorectal cancers without foci of adenoma.