A 44-year-old female was referred to our hospital with a complaint of abdominal fullness. Computed tomography(CT) showed multiple liver masses and a huge ovarian tumor. Colonoscopy revealed a type 4 advanced cancer in the sigmoid colon. She was diagnosed with unresectable liver and ovarian metastases from advanced sigmoid colon cancer, for which we were obliged to select chemotherapy. As the first line, FOLFOX was applied and performed for 6 cycles, followed by FOLFOX plus bevacizumab(BV)for 5 cycles. While no deterioration of liver and ovarian metastases was observed during the course of those chemotherapy regimens, the patient developed a considerable level of acute sensorimotor neuropathic symptoms associated with oxaliplatin-induced peripheral neurotoxicity, forcing us to replace FOLFOX plus BV with FOLFIRI plus BV. Three cycles of FOLFIRI plus BV, however, turned out to be progressive disease with deterioration of liver and ovarian metastases. Since her oxaliplatin-induced neurotoxicity was improved, a regimen of FOLFOX plus BV was once again applied to her for 3 cycles, which failed to prevent her from having a progressive disease. The sequencing of K-RAS genes from the biopsy specimens of sigmoid colon cancer revealed an expression of a wild-type K-RAS. Thus, an addition of panitumumab to FOLFOX was made. Surprisingly, after 3 cycles of the chemotherapy regimen over 3 months, a significant reduction in the size of liver and ovarian metastases was observed. Her sense of abdominal fullness was apparently reduced and was even lower than what it was at admission. Panitumumab has great potential for effective treatment of patients with unresectable stage IV colorectal cancer, even after having acquired resistance to prior chemotherapy regimens.