Transplantable malignant melanoma in LT.B6 congenic mice resembling pigmented epithelioid melanocytoma in humans.

Genetically engineered mouse models have been generated to recapitulate major signaling pathways deregulated in melanoma. Although these models are invaluable to delineate the relationship between gene mutations and targeted therapeutics, no spontaneously occurring melanomas are available in laboratory mice, which might be used to discover novel disrupted pathways, other than the widely studied MAPK, PI3-AKT and CDK4-INK4A-RB1. We report multiple spontaneously occurring melanomas on the tail of LT.B6 congenic strain, commonly used to study spontaneous ovarian teratomas. We present the evidence of spontaneous mouse melanoma and successful transplantation into 2 out of 2 mice, thereby enabling a complete histopathologic and clinical characterization. The histopathology of LT.B6 melanomas remarkably resembled a human melanoma subtype, pigmented epithelioid melanocytoma (PEM); and their clinical behavior was similar in indolent growth, metastasis to local lymph nodes and lack of liver metastasis. Lung metastasis was unique in the mice. Using qRT-PCR, we detected the expression of two melanocyte specific genes, Tyrp1 and Mitf, in the transplanted primary tumors and nodal metastases but not liver, confirming the histopathology. This mouse model closely resembled a low-grade variant of human melanoma and could provide the opportunity to globally investigate the genetic and epigenetic alterations associated with metastasis.