Chromosome 7 aneusomy. A marker for metastatic melanoma? Expression of theepidermal growth factor receptor gene and chromosome 7 aneusomy in nevi, primary malignant melanomas and metastases

Receptor tyrosine kinases such as the epidermal growth factor receptor (EGF R) play an important role in a variety of malignant neoplasias, making the search for aberrations in the relevant chromosomes an important issue. Diff erential expression of the EGFR gene was investigated by reverse transcript ase (RT)-PCR on tissue samples of normal skin, nevi, primary melanomas, and melanoma metastases. The EGFR gene is located on chromosome 7p12.3-p12.1. To determine the number of chromosomes 7 in cell nuclei of the mentioned ti ssue samples we performed fluorescence in situ hybridization (FISH) on touc h preparations, using a DNA probe that hybridizes specifically to the centr omeric region of chromosome 7. Additionally, chromosome 7 number in interph ase nuclei was determined in short-term primary cell cultures of nevi, prim ary melanomas, and metastases. The highest EGFR gene expression frequency w as found in melanoma metastases. By FISH we detected the highest fraction o f cell nuclei with more than two chromosomes 7 in the group of metastases. Our results suggest that overexpression of the EGFR gene might play an impo rtant role in metastasis of malignant melanoma. This is well reflected by p olysomy 7, possibly accounting for an increased EGFR gene copy number.