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Amplification and/or overexpression of genes encoding tyrosine kinase receptors KIT and ERBB2 have been reported in testicular germ cell tumors (TGCTs). These receptors can bind the adaptor molecule GRB7 encoded by a gene adjacent to ERBB2 at 17q12, a region also frequently gained in TGCTs. GRB7 binding may be involved in the activation of RAS signaling and KRAS2 maps to 12p, which is constitutively gained in TGCT and lies within a minimum overlapping region of amplification at 12p11.2-12.1, a region we have previously defined. RAS proteins activate BRAF, and activating mutations of genes encoding these proteins have been described in various tumors. Here we determine the relationships between expression levels and activating mutations of these genes in a series of 65 primary TGCTs and 4 TCGT cell lines. High levels of expression and activating mutations in RAS were mutually exclusive events, and activating mutations in RAS were only identified in the seminoma subtype. Mutations in BRAF were not identified. Increased ERBB2 expression was associated with differentiated nonseminoma histology excised from lymph nodes postchemotherapy. Mutation, elevated expression, and correlations between expression levels of KRAS2, GRB7, and KIT are consistent with their involvement in the development of TGCTs.

Activating mutations in exon 15 of BRAF have been detected in a high proportion of cutaneous melanomas. To determine whether such mutations are a feature of conjunctival or uveal melanomas, we screened DNA from these tumours. Twenty-one conjunctival and 88 uveal tumours were included in the study. Mutation analysis of BRAF exons 11 and 15 was undertaken using a combination of conformationally sensitive gel electrophoresis and direct sequencing. Mutations in exon 15 were detected in three of the conjunctival tumours (two V599E and one E585 K). None of the uveal tumours possessed a BRAF mutation in either exon 15 or 11. We conclude that uveal melanomas arise independently of oncogenic BRAF mutations, but the development of a proportion of conjunctival tumours involves mutation of this gene.