Loss of heterozygosity on long arm of chromosome 22 in sporadic colorectal carcinoma

AIM:The loss of heterozygosity(LOH)on tumorsuppressor genes is believed to play a key role incarcinogenesis of colorectal cancer.In this study,weanalyzed the LOH at 5 loci on the long arm ofchromosome 22 in sporadic colorectal cancer to identifyadditional loci involved in colorectal tumorigenesis.METHODS:Five polymorphic microsatellite markerswere analyzed in 83 cases of celorectal and normal DNAby PCR.PCR products were eletrophoresed on an ABI377 DNA sequencer;Genescan 3.1 and Genotype 2.1software were used for LOH scanning and analysis.Comparison between LOH frequency andclinicopathological data were performed by x~2 test.P<0,05 was considered as statistically significant.RESULTS:The average LOH frequency on chromosome22q was 28.38 %.The region between markersD22S280 and D22S274(22q12.2-q13.33)exhibitedrelatively high LOH frequency.The two highest LOH lociwith frequencies of 35.09 % and 34.04 % wasidentified on D22S280(22q12.2-12.3)and D22S274(22q13.32-13.33).8 cases showed LOH at allinformative loci,suggesting that one chromosome 22qhad been completely lost.On D22S274 locus,LOHfrequency of rectal cancer was 50 %(9/18),which washigher than that of proximal colon cancer(12 %,2/17)(P=0.018).The frequency of distal colon cancer was42 %(5/12),also higher than that of proximal coloncancer.But there was no statistical significance.Puttingboth the tumors in distal colon and rectum togetherinto consideration,the frequency,47 %(14/30),washigher than that of proximal colon cancer(P=0.015),suggesting the mechanism of carcinogenisis wasdifferent in both groups.CONCLUSIONS:This study provided evidence for theinvolvement of putaUve tumor suppressor genes relatedto the sporadic colorectal carcinoma on chromosome22q.The tumor-suppressor-gene(s)might locate on the22q12.2-12.3 and/or 22q13.32-13.33.