Zhongmin Guo

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 insight into the roles of genetic alterations in human carcinogenesis and clues to clonal origin of tumors. Intratumoral heterogeneity of genetic changes of cervical cancer has not been described so far. In this study, we analyzed the intratumoral heterogeneity of chromosome 3p deletions and X-chromosome inactivation patterns in multiple microdissected samples from each individual cervical cancer, attempting to understand the roles of 3p deletions in development of cervical cancer and its clonal origin. Totally, 120 normal and lesional samples from 14 cases of fresh cervical cancers were analyzed. Frequency and patterns of allelic losses of 3p were assessed by polymerase chain reaction (PCR) amplification of 12 microsatellite markers flanking the frequently deleted regions of 3p, followed by Genescan analysis in an ABI 377 DNA sequencer. Loss of heterozygosity was recorded as heterogeneous pattern (LOH present in parts of samples or LOH involving different alleles among different samples) and homogeneous pattern (LOH involving identical alleles in all samples from the tumor). Allelic loss affecting at least one marker was detected in 8 of 14 cases (57%). Allelic losses, both homogeneous and heterogeneous, were frequently detected at FHIT gene region (D3S1300, 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 tumors exhibited homogeneous allelic loss involving at least one of these three 3p loci. Allelic losses were present in the CIN lesions synchronous with invasive lesions positive for LOH. Our findings suggest essential roles of genes on these 3p loci, particularly the FHIT gene in participating in clonal selection and early development of cervical cancer. Most interestingly, with the combination of LOH analysis and X-chromosome inactivation analysis, we provided the first clear genetic evidence of polyclonal origin of cervical invasive cancer in two of eight cases. This finding strongly suggests the importance of field defect (possible human papilloma virus) in cervical carcinogenesis.

HPV typing and HPV16 E6-sequence variations in synchronous lesions of cervical squamous-cell carcinoma from Swedish patients

We microdissected 15 specimens of invasive cervical cancer co‐existing with some of its precursors. Out of 15 cases, 10 carried HPV16, 2 HPV31, 1 HPV18 and 2 were HPV‐negative. We found 3 HPV16 E6 variants among the 10 cases; one was A → G in nt 131 (one case) and a second was A → G in nt 276. The third, T ;→ G in nt 350, was common, and was found in 5 of the 10 patients infected by HPV16. The type of HPV and the E6 variant were identical in all lesions within the same patient. Viral DNA present in normal epithelium was identical in type and E6 variant to HPV in the same patients lesions. Multiple samples from invasive cancers with HPV were consistently positive. The data suggest that the originally infecting HPV, including its variant type in the E6 gene, persists unaltered in the whole series of CIN that precedes invasive cancer. Our data are compatible with an essential role of HPV manifested by persistence of the viral genome during the entire natural life history of cervical cancer. We did not confirm previous data on the specific association of invasive cancer with an HPV E6 variant (G at nt 350 rather than T). The discrepancy may depend on the relatively few cases investigated or selection of a special sub‐set with progression from CIN to invasive cancer already manifest. Int. J. Cancer 83:34–37, 1999.

Clonality analysis of multifocal carcinoid tumours of the small intestine by X-chromosome inactivation analysis

The clonality of intestinal carcinoids and the relationship between different tumour deposits of multiple intestinal carcinoids were investigated in this study. Six cases of multiple ileal carcinoids were selected for analysis and three independent carcinoid lesions from each case were microdissected. Clonality of the lesions was determined by polymerase chain reaction (PCR)‐based X‐chromosome inactivation of the human androgen receptor gene. Four out of six cases were heterozygous for microsatellite repeats within the androgen receptor gene and thus informative for the study. The results showed that all 12 lesions analysed had non‐random X‐chromosome inactivation (monoclonal) patterns, compared with the background normal intestinal mucosal tissues. This finding proves for the first time the monoclonal origin of human intestinal carcinoids, by X‐chromosome inactivation analysis. More interestingly, identical X‐chromosome inactivation patterns were found in different carcinoid lesions from each individual case. This evidence strongly indicates that multiple carcinoids of the small intestine were generated by metastasis of a primary tumour to different locations in the intestine, rather than being of multiple origin. This study provides an important insight into the carcinogenesis of intestinal carcinoids. Copyright

HPV16 E6 gene variations in invasive cervical squamous cell carcinoma and cancer in situ from Russian patients.

HPV16 is frequently seen in invasive cervical cancer (ICC) and cervical intraepithelial neoplasia (CIN). Its E6 gene has frequent sequence variations. Although some E6 variants have been reported to have different biochemical or biological properties, they do not show geographical identity. Moreover, the definition of ‘variant’ has been a source of confusion because it has been based on all departures from the ‘prototype’ once isolated randomly from an ICC case. We amplified the HPV16 E6 gene by PCR from fresh-frozen tissue of 104 cases of ICC and CIN from Russian patients and sequenced it in positive cases. We found that 32 of 55 (58.2%) ICC cases and 18 of 49 (36.7%) CIN cases were HPV 16-positive and we could identify 3 groups of E6 variants: group A was characterized by G at nt 350 where group B had T, and group M was a heterogeneous mixture of unique E6 variants; no significant difference existed in the distribution of the different groups between ICC and CIN; the clinically malignant (as defined by FIGO stage) order between the groups was M > A > B in ICC; in the cases with a single HPV16 E6 sequence, coexisting ICC, CIN and normal epithelium in the same patient shared the E6 variant; and 4 cases of ICC had double/multiple E6 variants. The results did not show any importance of E6 variants for ICC progression in Russian women. The results also indicated that the original HPV16 variant persisted during ICC progression, and that at a low frequency, double infections and/or mutation of variants might occur.

HPV-related Cancer Susceptibility and p53 Codon 72 Polymorphism

Conflicting results regarding the association of a polymorphism at codon 72 of the p53 tumour suppressor gene and susceptibility to develop human papilloma virus (HPV)-associated cervical cancer have been published over the last year, implicating differences in ethnic background, sample origin, sample size and/or detection assay. The material for this study was collected in the identical geographical region as for 2 previous reports with contradictory results regarding the association of codon 72 genotype with squamous cell cancer (SCC). We have used an alternative detection assay, based on pyrosequencing technology, that interrogates the variable position by the accuracy of DNA polymerase. In addition to cervical clinical specimens from SCC, HPV16- and HPV18-infected adenocarcinoma cases as well as cervical intraepithelial neoplasia (CIN) were investigated. No significant association was found between p53 codon 72 genotype and the risk to develop adenocarcinoma, SCC or CIN in the Swedish population.

Clonality of Precursors of Cervical Cancer and Their Genetical Links to Invasive Cancer

Two problems were the focus of this study. (1) Is precancer and/or invasive cancer of the human cervix a poly- or monoclonal proliferation of neoplastic cells? (2) Are simultaneously present precancers and cancers of the cervix clonally related, or do they arise independently? Microdissection of 37 neoplastic lesions with different degrees of histologic severity in 22 patients followed by polymerase chain reaction–based analysis of X-chromosome inactivation was used as a principal method. Invasive cancers were interpreted as monoclonal because samples invariably showed monoclonal signals. In two thirds of these cases, simultaneously present precursors had the identical X-chromosome inactivation pattern, but in one third the pattern was different. Polyclonality was seen in a subgroup of precursors, where there was no simultaneous presence of invasive cancer. In contrast, when invasive cancer was present, no precursor signaled polyclonality. Data taken together indicate that the pathogenesis of cervical cancer is probably even more complicated than that of other cancers involving selection of subclones from originally polyclonal precursors and possibility of coexistence of precursors of different monoclonal composition. The study also observed that a large field of normal cervical squamous epithelium (approximately 500 basal squamous epithelial cells) with nonrandom X-chromosome inactivation was present. It remains to be further investigated whether this phenomenon represents an embryologic lyonization pattern of X-chromosome inactivation or postembryologic clonal expansion of submorphologically transformed cells.

Oncogene lineages of human papillomavirus type 16 E6, E7 and E5 in preinvasive and invasive cervical squamous cell carcinoma.

Human papillomavirus (HPV)16 accounts for about 60% of the HPV infections in invasive cervical cancer (ICC). There are many sequence variations within HPV16, some of which have been associated with different biological properties, although no definite correlations have yet been established. However, the definition ‘variant’ has been a source of confusion in research and diagnosis, since it is based on all sequence deviations from a randomly selected prototype. This study has sequenced the HPV16 oncogenes E6, E7 and E5 from 61 Swedish cases with cervical intraepithelial neoplasia grade III (CIN III) or ICC. Clustering the sequence variations at the three common sites of variation (nucleotide 350 in E6, which has previously been associated with the progression from CIN III to ICC, and nucleotides 3979 and 4042 in E5) resulted in the distinction of three major oncogene lineages encompassing more than 95% of the cases, and two minor oncogene lineages. Simple comparison of the distribution of the individual variations or oncogene lineages between CIN III and ICC showed no significant difference, but the number of variations in addition to the three common ones was significantly higher in ICC. This novel classification scheme, based on the variations in the E6, E7 and E5 region, is considered to be a major improvement over the classical ‘prototype‐variant’ classification, and can help to clarify the interpretation of HPV sequence data in relation to the progression of cervical cancer. Copyright