Human malignant melanoma: detection of BRAF- and c-kit–activating mutations by high-resolution amplicon melting analysis

Summary 

Activating mutations in the BRAF kinase have been reported in a large number of cases of malignant melanoma. This suggests that therapy with specific RAF kinase inhibitors may find use in treating this disease. If the response to RAF kinase inhibition is dependent on the presence of an activated BRAF protein, it will be necessary to evaluate cases of malignant melanoma for the presence or absence of BRAF mutations. High-resolution amplicon melting analysis is able to detect single base-pair changes in DNA isolated from paraffin-embedded tissue sections and obviates the need for direct DNA sequencing. Results can be available within 48 hours. In this report, we used high-resolution amplicon melting analysis to evaluate 90 cases of malignant melanoma for BRAF mutations. Of these 90 cases, 74 were metastatic melanomas, 12 were primary cutaneous melanomas, and 4 were in situ melanomas. BRAF activation mutations were found in 43 cases (48%). Forty-one of these mutations were in exon 15. The mutations in exon 15 included V600E (34 cases), V600K (6 cases), and V600R (1 case). Two activating mutations were found in exon 11, G469V and G469R. The presence or absence of a BRAF mutation in the junctional component of an invasive melanoma was maintained in the invasive component. We also evaluated these 90 cases, as well as an additional 10 cases (total of 100) for the expression of c-kit. The majority of invasive and metastatic malignant melanomas did not express c-kit, although all in situ lesions and the junctional components of invasive lesions were strongly c-kit positive. Surprisingly, 2 cases of metastatic malignant melanoma (2%) showed strong and diffuse c-kit expression and contained a c-kit–activating mutation, L576P, as detected by high-resolution amplicon melting analysis and confirmed by direct DNA sequencing. These 2 c-kit mutation–positive cases did not contain BRAF mutations. The presence of a c-kit–activating mutation in metastatic malignant melanoma suggests that a small number of melanomas may progress by a somatic mutation of the c-kit gene. The presence of BRAF- and c-kit–activating mutations in malignant melanoma suggests new approaches to treating this disease involving specific tyrosine kinase inhibitors may prove worthwhile and that mutation analysis by high-resolution melting analysis might help guide therapy.

Keywords: Malignant melanoma, BRAF, c-kit, High-resolution melting analysis