NF1 and breast cancer: Lacking adequate functional neurofibromin in the Schwann cell progenitor pathway, NF1 patients are at higher risk for tumors including malignant peripheral nerve sheath tumors (MPNSTs), optic pathway gliomas (OPGs), rhabdomyosarcomas, neuroblastomas, gastrointestinal stromal tumors (GISTs), pheochromocytomas, carcinoid tumors, and breast cancer, among others.