High incidence of N and K-Ras activating mutations in multiple myeloma andprimary plasma cell leukemia at diagnosis

Using allele,specific amplification method (ARMS), a highly sensitive one-s tage allele specific PCR, we have evaluated the incidence of NRAS and KRAS2 activating mutations (codons 12, 13, and 61) in 62 patients with either mo noclonal gammopathy of undetermined significance (MGUS) or multiple myeloma . (MM), primary plasma-cell leukemia (P-PCL), and also in human myeloma cel l lines (HMCL). NRAS and/or KRAS2 mutations were found in 54.5% of MM at di agnosis (but in 81% at the time of relapse), in 50% of P-PCL, and in 50% of 16 HMCL. In contrast, the occurrence of such mutations was very low in MGU S and indolent MM (12.50%). Of note, KRAS2 mutations were always more frequ ent than NRAS. The validity of the technique was assessed by direct sequenc ing of cell lines and of some patients. Multiple mutations found in two pat ients were confirmed by subcloning exon PCR amplification products, testing clones with our method, and sequencing them. Thus, these early mutations c ould play a major role in the oncogenesis of MM and P-PCL. Hum Mutat 18:212 -224, 2001. (C) 2001 Wiley-Liss, Inc.