[Pathologically complete response for unresectable stage IV rectal cancer using systemic chemotherapy with panitumumab - a case report].

We report a case of rectal cancer resulting in a pathologically complete response of the primary tumor by systemic chemotherapy with panitumumab, a new endothelial growth factor receptor(EGFR)antibody. A 56-year-old man was diagnosed as having unresectable Stage IV rectal cancer with local invasion and lung metastasis, and underwent systemic chemotherapy by FOLFOX, combined with panitumumab as a first-line therapy. After 3 courses of FOLFOX and 3 courses of FOLFOX with panitumumab, the treatment regimen was changed to FOLFIRI with panitumumab to prevent peripheral neuropathy. After 5 courses of FOLFIRI with panitumumab, pelvic computed tomography(CT)revealed that the primary tumor was markedly reduced, and the intrapelvic direct invasion was resolved. On the post-treatment chest CT, lung metastasis had disappeared. A low anterior resection preserving the automatic nerves, the colonic J-pouch and anal anastomosis, was performed 20 days after the last chemotherapy. Although the whole tumor-like lesion of the specimen was sectioned macroscopically at 5-mm intervals, no vivid tumor cells were detected at the pathological examination. The patient's postoperative course was uneventful, and no recurrence occurred 5 months after the operation. The EGFR receptor antibody is reported to have a significant anti-cancer effect for colorectal cancer without the KRAS gene mutation. In cases with relatively large tumors especially, EGFR antibody can be an effective first-line treatment.