Methotrexate-induced hemothorax in a woman with low-risk metastatic gestational trophoblastic disease

•Patients with invasive mole have a risk of bleeding to fragility and vascularity of the tumor.•Some patients may experience life-threatening bleeding.•Chemotherapy of patients with invasive/metastatic mole may induce bleeding.•In our patient with pulmonary metastatic mole, massive hemorrhage occurred 2 h after the first dose of MTX.•Our patient was successfully treated with partial resection of the bleeding tumor and additional 2 cycles of MTX.