[Complete response of locally recurrent anorectal cancer to proton beam therapy alone--a case report].

We report a case of locally recurrent anorectal cancer treated with proton beam therapy (PBT) alone that led to a clinically complete response. A 70-year-old woman with paraparesis due to infantile paralysis underwent abdominoperineal resection (APR) and D3 lymphadenectomy for anorectal cancer (PERb, type 2, 50×40 mm, muc-tub1, M1a[lung], Stage IV a]. Three months after APR, right middle and right lower lobectomies were performed for synchronous lung metastases. Adjuvant chemotherapy was not administered. One year and 8 months after APR, computed tomography (CT) showed local recurrence of the tumor (29×28 mm), which contacted the right ischial spine. Pelvic exenteration combined with sacral resection was not performed because of the patient's poor performance status. PBT (70 Gy [RBE]/25 F/5 week) was administered for treatment of the recurred tumor. CT revealed that the tumor disappeared 1 year after PBT, which was defined as complete response. The patient is alive and has not experienced recurrence for 7 years.