NF1 and malignant peripheral nerve sheath tumor: Due to BDNF being a secretory protein, the supernatants of normal human Schwann cell, PNF cells, NF1-derived MPNST cells, and sporadic MPNST cell without knockdown of NCOR2, and the peripheral blood of 3 PNF patients and NF1-derived MPNST patients, were collected to detect the content of BDNF through ELISA.