NF1 and neurofibromatosis type 1: In support of this model, transforming growth factor β (TGF-β), one of the key signalling molecules involved in fibrosis, is secreted by mast cells upon stimulation by neoplastic Nf1–/– Schwann cells.49 This hypothesis led to the testing of the broad anti-fibrotic pirfenidone, which has proven efficacy for idiopathic pulmonary fibrosis, in Phase 2 trials in NF1 patients with advanced pNF but, unfortunately, no benefit of pirfenidone was reported50 (NCT00076102).