Somatic activation of KIT in distinct subtypes of melanoma.
OBJECTIVE
Melanomas on mucosal membranes, acral skin (soles, palms, and nail bed), and skin with chronic sun-induced damage have infrequent mutations in BRAF and NRAS, genes within the mitogen-activated protein (MAP) kinase pathway commonly mutated in melanomas on intermittently sun-exposed skin. This raises the question of whether other aberrations are occurring in the MAP kinase cascade in the melanoma types with infrequent mutations of BRAF and NRAS.


METHODS
We analyzed array comparative genomic hybridization data from 102 primary melanomas (38 from mucosa, 28 from acral skin, and 18 from skin with and 18 from skin without chronic sun-induced damage) for DNA copy number aberrations specific to melanoma subtypes where mutations in BRAF and NRAS are infrequent. A narrow amplification on 4q12 was found, and candidate genes within it were analyzed.


RESULTS
Oncogenic mutations in KIT were found in three of seven tumors with amplifications. Examination of all 102 primary melanomas found mutations and/or copy number increases of KIT in 39% of mucosal, 36% of acral, and 28% of melanomas on chronically sun-damaged skin, but not in any (0%) melanomas on skin without chronic sun damage. Seventy-nine percent of tumors with mutations and 53% of tumors with multiple copies of KIT demonstrated increased KIT protein levels.


CONCLUSIONS
KIT is an important oncogene in melanoma. Because the majority of the KIT mutations we found in melanoma also occur in imatinib-responsive cancers of other types, imatinib may offer an immediate therapeutic benefit for a significant proportion of the global melanoma burden.
Curtin
John A
JA
Comprehensive Cancer Center, University of California, San Francisco, San Francisco, CA 94143-0808, USA.
Busam
Klaus
K
Pinkel
Daniel
D
Bastian
Boris C
BC
D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001549:Benzamides; D014408:Biomarkers, Tumor / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000068877:Imatinib Mesylate; D007150:Immunohistochemistry; D008297:Male; D008545:Melanoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D046228:Microarray Analysis; D008875:Middle Aged; D009693:Nucleic Acid Hybridization; D010879:Piperazines / Q000627:therapeutic use; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D011743:Pyrimidines / Q000627:therapeutic use; D012878:Skin Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*
D000970:Antineoplastic Agents; D001549:Benzamides; D014408:Biomarkers, Tumor; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit