We here describe the first example of a cancer of unknown primary (CUP) patient with concomitant idi- opathic pulmonary arterial hypertension who was treated with docetaxel monotherapy. A 43-year-old woman was admitted to our hospital with left chest pain in June 2011. Based on the results of the general physical and other examinations, the patient was diagnosed as having CUP. The patient was treated with total doses of 40 Gy to a painful bone metastasis, followed by docetaxel mono- therapy at 60 mg/m 2 . Nine days after chemotherapy, she developed shortness of breath, and laboratory investiga- tions showed a substantial increase in serum amino-ter- minal pro-brain natriuretic peptide levels of 293.2 pg/ml (normal range, \125 pg/ml). At day 17, the right ventric- ular systolic pressure increased from 93 to 125 mmHg, suggesting right-sided heart failure, and consequently she died on day 21.
