NF1 and cancer: Research on the biologic basis of plexiform neurofibroma in NF-1 states that increasing evidence of loss of NF-1 expression in neoplastic Schwann cells is associated with elevated levels of activated ras, supporting the notion that the NF-1 gene product neurofibromin acts as a growth regulator by inhibiting ras protein activity (correlates with human cancer development and dysfunction of neurofibromin) [14].