Melanoma Hyperpigmentation Is Strongly Associated With KIT Alterations

Adverse cutaneous reactions to chemotherapeutic drugs

Drug reactions resulting from chemotherapy agents are common and frequently affect the skin. Although often benign, a select few of these cutaneous reactions may necessitate immediate changes to the antineoplastic regimens. Given the diversity of chemotherapeutic skin reactions and their complex implications on patient management, an organized conceptual schema is imperative for proper patient care. We evaluate a number of commonly seen chemotherapy-induced skin toxicities organized by pathogenic mechanism and drug class, providing a framework for the identification and categorization of adverse events to prevent unrecognition. Groupings of these reactions include direct cytotoxicity and/or drug accumulation, immunologic hypersensitivity, and aberrant molecular signaling.

Molecular dermatopathology in malignant melanoma

At present, immunohistochemistry is taken for granted in the establishment of malignant melanoma (MM) diagnosis. In recent years, molecular diagnosis in dermatopathology has benefited from a vast array of advances in the fields of genomics and proteomics. Sensitive techniques are available for detecting specific DNA and RNA sequences by molecular hybridization. This paper intends to update methods of molecular cytogenetics available as diagnostic adjuncts in the field of MM. Cytogenetics has highlighted the pathogenesis of atypical melanocytic neoplasms with emphasis on the activation of the mitogen-activated protein kinase (MAPK) signalling pathway during the initiation step of the neoplasms. 20 to 40% of MM families have mutations in the tumour suppressor gene p16 or CDKN2A. In addition, somatic mutations in p16, p53, BRAF, and cKIT are present in MM. Genome-wide scan analyses on MM indicate positive associations for genes involved in melanocytic naevi, but MM is likely caused by a variety of common low-penetrance genes. Molecular dermatopathology is expanding, and its use in the assessment of melanocytic neoplasms appears to be promising in the fields of research and diagnosis. Molecular dermatopathology will probably make its way to an increased number of diagnostic laboratories. The expected benefit should improve the patient management. This evolution points to a need for evolution in the training requirements and role of dermatopathologists.

The phosphatidyl inositol 3-kinase pathway is central to the pathogenesis of Kit-activated melanoma

Mouse Kit L575P, the ortholog of human KIT L576P, a common KIT mutation found in human melanoma was expressed in an immortalized but non-transformed mouse Ink4a-Arf-deficient melanocyte cell line. The resultant Ink4a-Arf-deficient Kit L575P-expressing melanocytes exhibited increased proliferation, the ability to grow in soft agar, and increased migration. When these cells were injected subcutaneously into NOD/SCID/gamma(c) mice, melanomas arose in 5 of 7 (71%) mice. One of seven mice (14%) injected with these cells developed metastatic disease. Evaluation of signal transduction pathways downstream of constitutively activated Kit L575P revealed striking activation of the phosphatidyl inositol 3-kinase (PI3K) pathway. Inhibition of the PI3K pathway pharmacologically or genetically abolished the transformation phenotypes gained by the L575P single mutant. These studies validate this Kit L575P-activated model of melanoma and establish the PI3K pathway as a dominant signaling pathway downstream of Kit in melanoma.