Analysis of p53 gene mutations and loss of heterozygosity for loci on chromosome 9q in basal cell carcinoma

Trisomy 6 in basal cell carcinomas correlates with metastatic potential: a dual color fluorescence in situ hybridization study on paraffin sections

BACKGROUND

Most basal cell carcinomas (BCCs) are indolent lesions; a few become locally aggressive or even metastatic. Little is known about the molecular and genetic alterations in this malignant transformation. Conventional karyotyping in BCC has revealed a high frequency of nonclonal, structural rearrangements, with few cases that show multiple, unrelated, small clones suggestive of a multicellular origin. Trisomy 6 was described recently in a few BCCs, but the biologic significance of the appearance of trisomy 6 in BBCs was not clear.

METHODS

Thirty cases including 4 metastatic, 4 locally aggressive, and 22 conventional nonaggressive BCCs were studied. Fluorescence in situ hybridization (FISH) was performed on 4 microm tissue sections, using alpha-centromeric enumeration probes for chromosome 6 (SpectrumGreen, Vysis Inc., Downers Grove, IL) and chromosome 4 (SpectrumOrange, Vysis Inc., Downers Grove, IL, used as disomic cell control). Trisomy 6 was semiquantitated within tumor cells and nonneoplastic cells in each case.

RESULTS

Trisomy 6 was identified in all 4 metastatic BCCs within tumor cells and in corresponding BCCs at the primary cutaneous site in 2 of these 4 cases. Two locally aggressive BCCs, 1 of which had preceding radiation exposure, also showed trisomy 6. All nonaggressive BCCs and nonneoplastic cells were disomic for chromosome 6.

CONCLUSIONS

Trisomy 6 has been identified as a cytogenetic aberration representative of tumor cells in aggressive and metastatic BCC. None of the nonaggressive BCCs in this study demonstrated trisomy 6. Acquisition of trisomy 6 by tumor cells in BCC may lead to the emergence of metastatic potential. Additional studies to define the underlying mechanisms may be valuable in preventing aggressive behavior in BCC.

Analysis of p53 and BAX mutations, loss of heterozygosity, p53 and BCL2 expression and apoptosis in basal cell carcinoma in Korean patients

BACKGROUND

Apart from some Japanese studies, there are few data on the gene mutations involved in the development of basal cell carcinomas (BCC) in Koreans or other Asians. Objective To gain insight into the molecular pathogenesis of BCC in Koreans.

METHODS

A collection of 33 cases of BCC were screened for mutations of p53 and BAX genes, p53 and BCL2 expression, loss of heterozygosity (LOH) and apoptosis.

RESULTS

Mutations of p53, found in 9% (three of 33) of the cases, were all mis-sense mutations (G-->C transversions) at codon 246 on exon 7. In 6% (two of 33), BAX gene showed frameshift mutations resulting from deletions in the poly(G) tract. LOH on chromosome 9q was seen in 58% (14 of 24), and p53 mutations developed only among the 9q LOH+ cases; LOH on chromosome 18q, where BCL2 gene is located, was found in 13% (four of 30). Immunohistochemical expression of p53 was seen in 27% (nine of 33), and its expression did not coincide with p53 mutations. BCL2 expression was seen in 39% (13 of 33). Apoptosis was revealed in 21%. In BCC, 9q LOH and p53 mutations seem to be closely related; the immunoreactivity of p53 and its mutations were not directly related; and p53 and BCL2 expression were negatively correlated. Frameshift mutations of the BAX gene in BCC are documented for the first time.

CONCLUSIONS

Various molecular mechanisms operate with redundant complexity in the pathogenesis of BCC. The LOH on chromosome 9q is the most frequent genetic alteration, as in other races; however, p53 mutations are much less frequent in Koreans than in Caucasians and suggest aetiologies other than ultraviolet radiation.

Nonrandom numerical chromosome abnormalities in basal cell carcinomas

Clonal chromosome abnormalities were found in 22 of 23 short-term cultured basal cell carcinomas (BCC) of the skin. The karyotypic abnormalities were nonrandom and in several cases included evidence of clonal evolution. Especially in cultures showing an epithelial growth pattern, simple numerical changes, most commonly +18, +9, +20, +7, and +5, predominated and presumably constitute pathogenetically important aberrations present in the neoplastic parenchyma. Also, several structural rearrangements of chromosome arm 9q were seen, which may be of particular interest against the background that a gene for familial BCC (Gorlin syndrome), the PTCH gene, maps to this region. Finally, most of the clonal aberrations detected in predominantly fibroblast-like cultures are likely to reflect changes acquired by cells of the tumor stroma, which raises the question whether mutations also of this tumor component may play a pathogenetic role in BCC development.

Differential allele loss on chromosome 9q22.3 in human non-melanoma skin cancer

Familial predisposition to basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin are apparent in the autosomal dominant syndromes naevoid basal cell carcinoma syndrome (NBCCS) and multiple self-healing squamous epitheliomata (MSSE) respectively. The gene responsible for NBCCS has been proposed to be a tumour-suppressor gene and is mapped to the same 2 Mb interval on 9q22.3 as the MSSE gene ESS1. In an attempt to further map the NBCCS gene, we have examined loss of heterozygosity (LOH) in 16 sporadic BCCs and two familial BCCs using microsatellite markers located within the candidate gene region. The overall frequency of LOH observed was 67% in the BCCs and partial or interstitial deletions were found in eight tumours, with the highest LOH frequency at markers D9S280, D9S287 and D9S180. To determine if the same genomic region also shows frequent LOH in tumours with a squamous phenotype, we have examined 11 SCCs, four actinic keratoses and 13 cases of Bowen's disease for LOH at 9q22.3. An overall LOH frequency of 50% was observed at D9S180, and occurred in all types of squamous tumours. In contrast, a much lower LOH frequency of only 6% was found at the D9S287 locus. Our observation of different patterns of LOH at 9q22.3 in sporadic BCCs and SCCs implies that more than one tumour-suppressor gene might be located in this genomic region.