Analysis of intratumoral heterogeneity of chromosome 3p deletions and genetic evidence of polyclonal origin of cervical squamous carcinoma

Investigation on intratumoral genetic heterogeneity provides an important i nsight into the roles of genetic alterations in human carcinogenesis and cl ues to clonal origin of tumors. Intratumoral heterogeneity of genetic chang es of cervical cancer has not been described so far. In this study, we anal yzed the intratumoral heterogeneity of chromosome 3p deletions and X-chromo some inactivation patterns in multiple microdissected samples from each ind ividual cervical cancer, attempting to understand the roles of 3p deletions in development of cervical cancer and its clonal origin. Totally, 120 norm al and lesional samples from 14 cases of fresh cervical cancers were analyz ed. Frequency and patterns of allelic losses of 3p were assessed by polymer ase chain reaction (PCR) amplification of 12 microsatellite markers flankin g the frequently deleted regions of 3p, followed by Genescan analysis in an ABI 377 DNA sequencer. Loss of heterozygosity was recorded as heterogeneou s pattern (LOH present in parts of samples or LOH involving different allel es among different samples) and homogeneous pattern (LOH involving identica l alleles in all samples from the tumor). Allelic loss affecting at least o ne marker was detected in 8 of 14 cases (57%). Allelic losses, both homogen eous and heterogeneous, were frequency detected at FHIT gene region (D3S130 0, 40% and 60%; D3S4103, 27.3% and 54.6%), 3p21.3-21.2 (D3S1478, 27.3% and 45.5%), and 3p24.2-22 (D3S1283, 30% and 50%). Seven of eight LOH-positive t umors exhibited homogeneous allelic loss involving at least one of these th ree 3p loci. Allelic losses were present in the CIN lesions synchronous wit h invasive lesions positive for LOH. Our findings suggest essential roles o f genes on these 3p loci, particularly the FHIT gene in participating in cl onal selection and early development of cervical cancer. Most interestingly , with the combination of LOH analysis and X-chromosome inactivation analys is, we provided the first clear genetic evidence of polyclonal origin of ce rvical invasive cancer in two of eight cases. This finding strongly suggest s the importance of held defect (possible human papilloma virus) in cervica l carcinogenesis.