CHROMOSOMAL ALLELE LOSS IN PRIMARY CUTANEOUS MELANOMA IS HETEROGENEOUS AND CORRELATES WITH PROLIFERATION

Loss of heterozygosity at specific loci in neoplastic cells suggests t he presence of a tumor suppressor gene within the deleted region. Usin g the microdissection technique, loss of heterozygosity has been ident ified in paraffin-embedded primary melanomas on chromosomes 1p and 9q. Our purpose was to determine loss of heterozygosity in primary cutane ous melanomas and to relate chromosomal alterations with cell morpholo gy and proliferation of the tumor. Two to seven morphologic different areas in 12, primary cutaneous high risk melanomas (Breslow > 1.5 mm), as well as adjacent normal tissue, were microdissected and subjected to single step DNA extraction. Extracted genomic DNA was amplified by polymerase chain reaction using two polymorphic markers on chromosomes Ip (D1S450, between D1S548 and D1S228) and 9q (D9S12). Proliferation was evaluated by MIB-1 (Ki67) immunoreactivity and cell morphology, pi gmentation and inflammation surrounding microdissected areas were inve stigated by microscopic inspection of hematoxylin and eosin stained se ctions. Twelve of 34 different areas (35%) showed loss of heterozygosi ty with at least one marker. Two of 32 areas showed loss of heterozygo sity with D1S450 (two areas noninformative), seven of 30 with D9S12 (f our areas noninformative), and three areas showed loss of heterozygosi ty at both loci. In three of these cases, analysis of different tumor foci revealed areas with/without loss of heterozygosity. In these case s, the percentage of MIB-I-positive cells was at least four times high er in areas with loss of heterozygosity compared with areas without lo ss of heterozygosity. Most areas with loss of heterozygosity consisted of small cuboidal to epitheloid cells. Spindle shaped and large anapl astic cells showed loss of heterozygosity less frequently. Neither mel anization of tumor cells nor the presence of inflammation had an influ ence on the frequency of loss of heterozygosity. Primary cutaneous mel anomas show intratumoral morphologic and chromosomal heterogeneity. Lo ss of heterozygosity on chromosomes 1p and 9q correlated with cell pro liferation, suggesting that selected cell clones are responsible for t umor progression.