Cells are sterile, validated by short tandem repeat profiling, and are tested as negative for mycoplasma. It is recommended that cell lines are tested for mycoplasma contamination and short tandem repeat (STR) profiling every 10 passages or each time a frozen seed stock is made. See cell culture protocol for additional details. WM266-4 is a metastatic human melanoma cell line with small flat mesenchymal morphology. This cell line was derived from the same patient as the cell lines WM115, WM293A, and WM165-1. WM115 cell line originated from the primary tumor, and WM266-4, WM165-1 and WM293A were from individual lymph-node metastases. The subject (55-year-old female) displayed VGP with a Clark level III tumor with thickness of 2.24mm.This cell line features the specific V600D (Val600Asp) mutation at codon 600 in the BRAF gene. This cell line also expresses PTEN loss of function including hemizygous deletion. WM266-4 cell line is wild type for N-RAS, c-KIT, and CDK4 genes. WM266-4 cells produce xenograft tumors when injected into immunocompromised mice.