Relationship between DNA ploidy-related parameters and the deletions in mismatch repair genes MLH1 and MSH2 in lentigo maligna and malignant melanomas.

Defects in DNA mismatch repair genes MLH1 and MSH2, first described in hereditary nonpolyposis colon cancer (HNPCC), have been postulated to be responsible for malignant transformation in several tumours. To date there are no data on cutaneous tumours. Using a PCR assay it was possible to identify deletions in MSH2 (exonic regions 12 and 13) in 16 of 47 lentigos maligna and in 10 of 36 malignant melanomas. Deletions in MLH1 (exonic regions 15 and 16) were found in 11 of 47 lentigos and in 15 of 36 melanomas. Comparison of DNA ploidy-related parameters between lentigos with and without exonic deletions in MSH2 and MLH1 did not show any significant differences. In contrast, melanomas positive and negative for exons 12 and 13 (MSH2) (26/36 and 10/36, respectively) differed significantly with respect to the percentages of diploid cells (P = 0.0179) and tetraploid cells (P = 0.0042). Comparison of melanomas positive and negative for exons 15 and 16 (MLH1) (21/36 and 15/36, respectively) showed significant differences in the percentage of aneuploid cells between 2c and 4c (P = 0.0141) and tetraploid cells (P = 0.0404). In summary, deletions in DNA mismatch repair proteins MSH2 and MLH1 were present both in lentigo maligna and in melanomas and correlated with DNA ploidy-related parameters in malignant melanomas.