Consistent with this notion of context specificity and potential promiscuity, prior work has suggested neurofibromin may regulate different, or multiple, Ras proteins across different cell lineages: Neurofibromin primarily acts on both HRAS and KRAS in melanoma (28) while KRAS alone is the critical effector in mast cells (29) or glioma (30). This evidence concerns the gene HRAS and melanoma.