Distal deletion of 1p in colorectal tumors: an initial event and/or a step in carcinogenesis? Study by fluorescence in situ hybridization interphase cytogenetics.

Cytogenetics studies have suggested that short arm deletion in chromosome 1 is involved in triggering colorectal tumor development. To elucidate the role of 1p under-representation in the tumoral process, we investigated by fluorescence in situ hybridization interphase cytogenetics, using simultaneously centromeric and p36 telomeric probes for chromosome 1, 27 primary adenocarcinomas, 5 metastases, 5 adenomas and as control 4 normal mucous membranes. The 1p under-representation in paradiploid tumoral cells, interpreted as a 1p deletion, was observed in 8/27 adenocarcinomas, 2/5 metastases and 3/5 adenomas. Thus, in diploid cells 1p deletion was observed in some tumors independently of the stage of the process. The 1p under-representation in total number of examined cells, i.e., diploid and aneuploid, was observed in 14/16 grade B1-B2 tumors, in 5/8 grade C1-C2 tumors, and all grade D tumors (3/3) and all metastases (5/5). There were no correlations with location or histological characteristics of cancers, gender or age of patients. These results show high frequency of 1p under-representation in intestinal tumors, and lead to separate the under-representation of 1p in diploid cells, which correspond to a 1p deletion probably implicated in the initiation of the process, from the under-representation in aneuploid cells, which mainly may be the consequence of complex rearrangements in relation to extension of the malignant process.