Detection of DDR2 mutations in malignant melanoma: A potentially targetable feature of advanced stage disease.

Abstract

9100 Background: The discoidin domain receptor tyrosine kinase 2 (DDR2) gene is mutated in a subset of non-small cell carcinoma of the lung. In lung cancer, targeting of DDR2 with the inhibitor dasatinib has been shown to inhibit DDR2-mutated cell line growth. Responses to dasatinib in DDR2-mutated lung tumors are currently being investigated in clinical trials. We investigated whether somatic DDR2 mutations also occur in melanomas using a set of different clinical subtypes bearing a variety of melanoma-associated molecular alterations. Methods: DNA was extracted from macrodissected FFPE sections of 168 melanomas and subjected to next-generation sequencing using a custom-designed 36-amplicon panel including the coding regions of DDR2 and exons 11 and 15 of BRAF. PCR products were prepared by Access Array, sequenced on the Ion Torrent PGM, and analyzed using Sequence Pilot software. All DDR2 mutations were confirmed by bidirectional Sanger sequencing. Relative expression analysis of the DDR2 gene was performed using RT-PCR on RNA extracted from FFPE sections, with levels normalized to ABL1 and GAPDH. Results: Heterozygous DDR2 point mutations were identified in 3.4% of BRAF-mutated melanoma (n=117) but not in any cases that lacked BRAF mutations (n = 51). All DDR2-mutated melanomas were advanced stage with lymph node and/or extensive soft tissue involvement and included both BRAF V600K and V600E cases. In contrast to the range of mutation sites reported in lung cancers, DDR2 mutations in melanoma (I488S, F574C, S667F and L701F) were at highly evolutionarily conserved positions in the kinase domain. The mutations are expected to be disruptive and may therefore modulate kinase activity. DDR2 transcripts were expressed in tumor cells in all mutated cases. Conclusions: DDR2 mutations in advanced stage melanoma may provide a targetable genetic feature for tyrosine kinase inhibitors such as dasatinib. The invariant association of DDR2 mutation with activating BRAF mutations suggests synergy in transformation between these distinct signaling pathways.