Clinicopathological And Molecular Genetic Study Of Chinese Hereditary Nonpolyposis Colorectal Cancer (HNPCC)

Objectives:To study the characteristics of the germ-line mutations of hMLH1 and hMSH2 genes in Chinese HNPCC families' probands or patients.Compare the difference of the clinicopathological features between the mutation positive families and the negative based on different clinical criteria. Identifythe relationship between mutation status and clinicopathological feature.Discuss the clinical value of the different clinical criteria.Methods:Among 116 HNPCC families analyzed,32 fulfilling Amsterdam Criteria (group AC),28 families fulfilling Fudan Recommend Criteria(group FD)and the rest fit Bethesda Guidelines(group BG).19 exons of hMLH1 and 16 exons of hMSH2 were directly sequenced in the 116 families' probands.Divive the three groups into different subgroups according to the mutation status (positive or negative).Results:(1).32 germ-line mutations were found in all 116 families' probands (mutation detection rate 27.6%),16 for hMLH1 and 16 for hMSH2,group AC has 16,group FD has 8 and group BG has 8.There was a wide spectrum of mutation type including 14 missense,7 nonsense,4 splice site,2 frame insertion or deletion and 5 frame shift mutations.Among the 16 mutations of hMLH1,exon12 and exon15 has three mutations each.Among the 16 mutations of hMLH2,exon7 has six and exon14 has four mutations. (2).32 families of group AC versus 28 families of group FD:there are only two significant clinical differences between these two groups,more synchronous and metachronous multiple relative tumours(21.6%vs.6%, P=0.001) were found in AC group,while more extracolorectal tumours (18.3%vs.55.8%,P=0.000) were found in FD group.Other features such as earlier age of onset for all colorectal cancers and all tumours,the ratio of proximal colonic cancers,the ratio of synchronous and metachronous multiple colon cancers,the ratio of mucinous carcinoma and the ratio of stageⅢⅣcolon cancer were similar.The sensitivity of Amsterdam Criteria is 50%,specificity is 81%and Youden's index is 31%. On the other hand,the sensitivity of Fudan Recommend Criteria is 75%, specificity is 58%and Youden's index is 33%.(3).Divide group AC into two groups,group AC1(mutation positive) and group AC2(mutation negative).There were no significant differences of the clinicopathological features such as earlier age of onset for all colorectal cancers and all tumours,the ratio of proximal colonic cancers, the ratio of synchronous and metachronous multiple colon cancers,the ratio of synchronous and metachronous multiple relative tumours,the ratio of extracolorectal tumours the ratio of mucinous carcinoma and the ratio of stageⅢⅣcolon cancer between these two groups(4).Divide group AC into two groups,group FD1(mutation positive) and group FD2(mutation negative).The ratio of synchronous and metachronous multiple relative tumours was higher in group FD1 than in group FD2(15.8% vs.1%,P=0.05).There were no other significant differences between two groups.(5).Among the five conditions of Bethesda Guidelines,there was a closely relation between the second conditions and the gene mutation status, positive or negative(P=0.014).(6).Families with hMSH2 mutation had a higher ratio of synchronous and metachronous multiple colon cancers than families with hMLH1 mutation (33%vs.6%,P=0.04).Conclusions:(1).hMLH1 and hMSH2 mutations in this group of HNPCC show a wide spectrum of distributions and mutation types,hMLH1 mutations were mainly located on exon12 and exon15,while exon7 and exon14 were the hot spots of hMLH2 mutations.(2).Fudan Recommend Criteria had a little higher sensitivity and accuracy than Amsterdam Criteria.Families fulfilling these two criterias share almost the same clinicopathological features.These show that Fudan Recommend Criteria play an important role in the diagnosis of Chinese HNPCC.In addition,multiple relative tumours in families fulfilling Fudan Recommend Criteria indicate high possibility of mutation positive.(3).The mutation negative families fulfilling Amsterdam Criteria had similar clinicopathological features as the mutation positive families. This indicate these families need some further tests such as hMSH6 and large deletion,they also need to follow the same follow-up and treatment strategy.We may find some new mutation types even some new genes from these families.(4).Among the five conditions of Bethesda Guidelines,the second conditions play an important role in the gene mutation status,positive or negative.This result tell us the five conditions may have different weight,we may make it more complete.(5).The HNPCC families with synchronous and metachronous multiple colon cancers may test the hMSH2 gene first.