HISTOLOGY AND HISTOPATHOLOGY

Cellular and Molecular Biology

 

Frequent intra-tumoural heterogeneity of promoter hypermethylation in malignant melanoma

M. Rastetter1, U. Schagdarsurengin1, C. Lahtz1, E. Fiedler2, W.Ch. Marsch2, R. Dammann1 and P. Helmbold2,3

1AWG Tumour Genetics of the Medical Faculty and 2Department of Dermatology, Martin Luther University Halle - Wittenberg, Germany and 3Department of Dermatology, Ruprecht-Karls University, Heidelberg, Germany

Offprint requests to: Reinhard Dammann, PhD, Institute for Human Genetics and Medical Biology, Martin Luther University Halle - Wittenberg, Magdeburger Str. 2, D-06097 Halle (Saale), Germany. e-mail: reinhard.dammann@medizin.uni-halle.de
Drs. Dammann and Helmbold contributed equally to this article



Summary. To investigate intra-tumoural coexistence and heterogeneity of aberrant promoter hypermethylation of different tumour suppressor genes in melanoma, we analyzed the intra-tumoural distribution of promoter methylation of RASSF1A, p16, DAPK, MGMT, and Rb in 339 assays of 34 tumours (15 melanoma primaries, 19 metastases) by methylation-specific PCR, correlation to histopathology and RASSF1A expression. We detected promoter hypermethylation of at least one gene in 74% of tumours (30%, 52%, 33%, 20%, and 40% for RASSF1A, p16, DAPK, MGMT and Rb, respectively). 70% of the cases exhibited an inhomogeneous methylation pattern (17%, 45%, 33%, 20%, and 40% for RASSF1A, p16, DAPK, MGMT and Rb, respectively). Samples from the core of the tumours represented the methylation state of the whole tumours more accurately than the periphery. Local intra-tumoural correlation was found between the promoter hypermethylation state of p16 and Rb or p16 and DAPK, or epitheloid tumour cell type and RASSF1A or p16 methylation. Mitosis rate and sex was correlated with methylation of RASSF1A. Histological results confirmed that promoter hypermethylation of RASSF1A led to aberrant expression patterns. We conclude that intra-tumoural inhomogeneity of promoter hypermethylation is frequent in melanoma and this supports the hypothesis of clonal instability during progression of melanomas. In prognosis studies, missing the intra-tumoural sample representativeness may result in a reduction of the sensitivities or specificities. Histol Histopathol 22, 1005-1015 (2007)

Key words: Melanoma, Tumor suppressor, Intra-tumoral heterogeneity, Epigenetic inactivation

DOI: 10.14670/HH-22.1005