Pulmonary hypertension (PH) induced by pulmonary tumor thrombotic microangiopathy (PTTM) can be fatal because its rapid progression confounds diagnosis, and it is difficult to control with therapy. Here we describe a woman with symptomatic PTTM-PH accompanying gastric cancer that was suspected from perfusion scintigraphy. PTTM-PH was diagnosed by gastroesophageal endoscopy and lung biopsy after partial control of PH using the platelet-derived growth factor (PDGF) receptor (PDGFR) tyrosine kinase inhibitor, imatinib. Treatment with sildenafil and ambrisentan further decreased PH, and she underwent total gastrectomy followed by adjuvant TS-1 chemotherapy. PH did not recur before her death from metastasis. Postmortem histopathology showed recanalized pulmonary arteries where the embolized cancer masses disappeared. PDGF-A, -B, and PDGFR-α, β expression was detected in cancer cells and proliferating pulmonary vascular endothelial cells. Thus, PTTM-PH was successfully controlled using a combination of imatinib, drugs to treat pulmonary arterial hypertension, and cancer management.