[Analysis of genetic disorders of cancer of the rectum: differences in relation to cancer of the colon].
OBJECTIVE
We studied the mechanisms of colon and rectal carcinogenesis by analysing in a series of 83 rectal tumors the prevalence of the two tumor types characteristic of colon cancer, i.e., the LOH+ type, defined by p53 and APC mutations (studied by DGGE and protein truncation assay), and the RER+ type, which is characterized by the instability of some mononucleotide repeat microsatellites (Bat 25 and Bat 26). Additionally, we analyzed the occurrence of Ki-Ras mutations (direct sequencing).


RESULTS
Only one tumor turned out to be RER+. Moreover, in 59% of the tumor cases mutations were found in p53, essentially affecting codon 175. The APC and Ki-Ras genes were found to be mutated in 40 and 26% of the rectal tumors, respectively. In 18 tumors (21%) none of the genes studied were mutated.


CONCLUSIONS
The RER+ phenotype is rare among rectal tumors, which are essentially LOH+. In these LOH+ tumors the p53 gene is more frequently mutated than in colorectal tumors with the same phenotype. Mutations in the APC and Ki-Ras genes, on the other hand, are less frequent in rectal tumors. Tumors with the RER- and LOH- phenotype may develop as a result of a third carcinogenesis model which must be defined.
Rebischung
C
C
INSERM U434-CEPH, Paris.
Laurent-Puig
P
P
Gerard
J P
JP
Thomas
G
G
Hamelin
R
R
D000368:Aged; D003110:Colonic Neoplasms / Q000235:genetics*; D005260:Female; D017491:Genes, APC / Q000235:genetics*; D016158:Genes, p53 / Q000235:genetics*; D011905:Genes, ras / Q000235:genetics; D005838:Genotype; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D010641:Phenotype; D012004:Rectal Neoplasms / Q000235:genetics*
Analyse des altérations génétiques du cancer du rectum: différences par rapport au cancer du côlon.