PIK3CA and malignant peripheral nerve sheath tumor: In our review, we identified 5 mutations in 4 MPNST tumors (17%) that would be expected to be both pathogenic and activating of the Ras pathway, including hotspot mutations in HRAS, PIK3CA, and FGFR1 and inactivating mutations in negative Ras regulators RASA1 and CNKSR2.