Relevance of Ras gene mutations in the context of the molecular heterogeneity of multiple myeloma.

Ras gene mutations are a recurrent genetic lesion in multiple myeloma (MM). Here, we report a mutation analysis of N- and K-Ras genes in purified plasma cell populations from a panel of 81 newly diagnosed MM patients stratified according to the most frequent genetic and molecular features associated with the neoplasia. Ras gene mutations, mostly involving the N-Ras gene, were detected in 20% of the patients. Ras mutations did not correlate with the presence of chromosome 13q deletion, trisomy of chromosome 11, 1q amplification or hyperdiploidy. In addition, despite an appreciable association with tumours overexpressing Cyclin D1, Ras mutations did not correlate at significant levels with any of the proposed groups in the TC classification, based on the presence of the major IgH chromosomal translocations and expression of Cyclin D genes. Finally, transcription analyses revealed the presence of differentially expressed transcripts in human multiple myeloma cell lines carrying the Ras gene mutations but not in primary tumours. Overall, these data suggest that Ras gene mutations are not likely to represent a master lesion in MM but its relevance needs to be considered in the context of other genetic abnormalities.