NF1 and plexiform neurofibroma: Nf1-deficient SKPs also have the capacity to form pNFs or cNFs, which appears to be contingent on their local microenvironment, and these cells exhibit the same properties as the embryonic Schwann cell progenitors that give rise to pNFs.29,30 These observations revealed that loss of Nf1 gene expression in SKPs is required, but not sufficient, for neurofibroma development, and revealed critical roles for the tumour microenvironment.