A 64-year-old woman with anorexia and anemia was diagnosed with ascending colon cancer invading the duodenum. Considering the difficulty of curative resection, we first performed gastrojejunostomy and ileostomy. After surgery, the patient received FOLFIRI with cetuximab as neoadjuvant chemotherapy. After 9 courses of the regimen, enhanced computed tomography revealed shrinkage of the lesion, with the efficacy evaluated as a partial response. The patient underwent right hemico- lectomy and partial resection of the duodenum. The pathological diagnosis was pT3(SS), pN0(0/30), ly1, v1, pPM0, pDM0, pRM0, fStage II . On histopathological examination, the efficacy of chemotherapy was evaluated as Grade 1a. The patient received adjuvant chemotherapy with FOLFIRI and remains well without any evidence of recurrence more than 6 months after surgery.