Genetics

Limited data are available on molecular genetic alterations in appendiceal tumours, and these data indicate similarities to those in colorectal tumours. KRAS mutations have been identified in approximately 70% of appendiceal muci-nous adenomas, mostly in codon 12 and a few in codon 13 {1871}. In addition, KRAS mutation has been identified in an appendix cystadenoma associated with a long history of ulcerative colitis {1123}. Tumour suppressor gene allelic imbalances have been found in about half of appendiceal mucinous adenomas with loss of heterozygosity (LOH) at several chromosomal loci, including 5q22, 6q, 17p13, and 18q21. LOH was most fre-

Fig. 5.09 Hyperplastic polyp of appendix. Cytological abnormalities of intraepithelial neoplasia are absent.

quent at the 5q locus linked to the APC tumour suppressor gene which in the colorectum is strongly associated with transition to adenoma {1871}. In cases of pseudomyxoma peritonei (well differentiated mucinous adenocarcinoma), LOH at one or two polymorphic microsatellite loci was seen in approximately half of the cases and was considered an indication of monoclonality.

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