Cytogenetic and interphase FISH analyses of 73 basal cell and three squamous cell carcinomas: different findings in direct preparations and short-term cell cultures

[Analysis of cytogenetic abnormalities in squamous cell carcinoma by array comparative genomic hybridization]

INTRODUCTION

Few conventional cytogenetic studies of squamous cell carcinoma (SCC) have been performed to date. The introduction of cytogenetic techniques such as comparative genomic hybridization (CGH) has resolved some of the problems associated with conventional cytogenetics. The aim of this study was to analyze the presence of genetic abnormalities in a series of patients with SCC using the technique of array CGH.

MATERIAL AND METHODS

The study included 8 patients (7 men and 1 woman; mean age, 75 years) diagnosed with primary SCC. DNA was extracted from frozen tissue and analyzed by array CGH.

RESULTS

All cases had genetic alterations, with gains more frequent than losses. The chromosomal regions with gains, in descending order of frequency, were as follows: 5p15.2, 9q31.3-q33.2, 13q, 18q22, 1p21-p22, 1q24-q25, 3p13, 4q33-q34 (HMGB2, SAP30), 20p12.2 (JAG1), 21q21.1, and Xq21.33. The region 9p13.1-p13.3 was the only one to display recurrent loss. No correlation was observed between the presence of gains or losses and the clinical and pathological characteristics of the tumors.

CONCLUSIONS

This is the first study to use the technique of array CGH to analyze genetic alterations in SCC. The finding of certain previously described aberrations (gain of 5p) suggests the existence of recurrent abnormalities. Likewise, the observation of alterations in small regions of chromosome 1 highlights the sensitivity of the technique to detect small changes. Application of the technique to a larger series of cases will provide greater insight into the genetic abnormalities implicated in the process of tumorigenesis in SCC.

Chromosome 6p amplification and cancer progression

Chromosomal imbalances represent an important mechanism in cancer progression. A clear association between DNA copy-number aberrations and prognosis has been found in a variety of tumours. Comparative genomic hybridisation studies have detected copy-number increases affecting chromosome 6p in several types of cancer. A systematic analysis of large tumour cohorts is required to identify genomic imbalances of 6p that correlate with a distinct clinical feature of disease progression. Recent findings suggest that a central part of the short arm of chromosome 6p harbours one or more oncogenes directly involved in tumour progression. Gains at 6p have been associated with advanced or metastatic disease, poor prognosis, venous invasion in bladder, colorectal, ovarian and hepatocellular carcinomas. Copy number gains of 6p DNA have been described in a series of patients who presented initially with follicle centre lymphoma, which subsequently transformed to diffuse large B cell lymphoma. Melanoma cytogenetics has consistently identified aberrations of chromosome 6, and a correlation with lower overall survival has been described. Most of the changes observed in tumours to date map to the 6p21-p23 region, which encompasses approximately half of the genes on all of chromosome 6 and one third of the number of CpG islands in this chromosome. Analyses of the genes that cluster to the commonly amplified regions of chromosome 6p have helped to identify a small number of molecular pathways that become deregulated during tumour progression in diverse tumour types. Such pathways offer promise for new treatments in the future.

Cytogenetic alterations in nonmelanoma skin cancer: a review

Since the advent of cytogenetic analysis, knowledge about fundamental aspects of cancer biology has increased, allowing the processes of cancer development and progression to be more fully understood and appreciated. Classical cytogenetic analysis of solid tumors had been considered difficult, but new advances in culturing techniques and the addition of new cytogenetic technologies have enabled a more comprehensive analysis of chromosomal aberrations associated with solid tumors. Our purpose in this review is to discuss the cytogenetic findings on a number of nonmelanoma skin cancers, including squamous- and basal cell carcinomas, keratoacanthoma, squamous cell carcinoma in situ (Bowen's disease), and solar keratosis. Through classical cytogenetic techniques, as well as fluorescence-based techniques such as fluorescence in situ hybridization and comparative genomic hybridization, numerous chromosomal alterations have been identified. These aberrations may aid in further defining the stages and classifications of nonmelanoma skin cancer and also may implicate chromosomal regions involved in progression and metastatic potential. This information, along with the development of newer technologies (including laser capture microdissection and comparative genomic hybridization arrays) that allow for more refined analysis, will continue to increase our knowledge about the role of chromosomal events at all stages of cancer development and progression and, more specifically, about how they are associated with nonmelanoma skin cancer.

Molecular cytogenetic analysis of basal cell carcinoma DNA using comparative genomic hybridization

In an attempt to define genomic copy number changes associated with the development of basal cell carcinoma, we investigated 15 sporadic tumors by comparative genomic hybridization. With the incorporation of tissue microdissection and degenerate oligonucleotide primed-polymerase chain reaction we were able to isolate, and then universally amplify, DNA from the tumor type. This combined approach allows the investigation of chromosomal imbalances within a histologically distinct region of tissue. Using comparative genomic hybridization we have observed novel and recurrent chromosomal gains at 6p (47%), 6q (20%), 9p (20%), 7 (13%), and X (13%). In addition comparative genomic hybridization revealed regional loss on 9q in 33% of tested tumors encompassing 9q22.3 to which the putative tumor suppressor gene, Patched, has been mapped. The deletion of Patched has been indicated in the development of hereditary and sporadic basal cell carcinomas. The identification of these recurrent genetic aberrations suggests that basal cell carcinomas may not be as genetically stable as previously thought. Further investigation of these regions may lead to the identification of other genes responsible for basal cell carcinoma formation.