A 42-year-old man was admitted because of huge retrovesical mass. The organ from which the tumor originated was unknown. The biopsy specimen showed poorly differentiated adenocarcinoma. The tumor increased rapidly and could not be resected because of peritoneal dissemination. The mass fully occupied the abdominal space with marked dyspnea. Fortunately, a marked decrease in the tumor size was noted by neo-MFC without any side effect. Therefore, the patient could enjoy a daily life until he died suddenly of cardiac failure 8 months after first admission. Retrovesical tumor is usually discovered at advanced stage because of lack of symptoms. For recovery of good performance status combined chemotherapy with relatively mild side effect must be selected and administered for a long time.