The present disclosure relates to the use of 1-[4-bromo-5-[1-ethyl-7-(methylamino)-2-oxo-1,2-dihydro-1,6-naphthyridin-3-yl]-2-fluorophenyl]-3-phenylurea or 1-(5-(7-amino-1-ethyl-2-oxo-1,2-dihydro-1,6-naphthyridin-3-yl)-4-bromo-2-fluorophenyl)-3-phenylurea in the treatment of cancers. Specifically, the disclosure is directed to methods of inhibiting PDGFR kinases and treating cancers and disorders associated with inhibition of PDGFR kinases including lung adenocarcinoma, squamous cell lung cancer, glioblastoma, pediatric glioma, astrocytomas, sarcomas, gastrointestinal stromal tumors, malignant peripheral nerve sheath sarcoma, intimal sarcomas, hypereosinophilic syndrome, idiopathic hypereosinophilic syndrome, chronic eosinophilic leukemia, eosinophilia-associated acute myeloid leukemia, or lymphoblastic T-cell lymphoma.