A 69-year-old man with a history of distal gastrectomy for early gastric cancer consulted our department concerning a possible diagnosis of sigmoid colon cancer. After detailed examination, he was diagnosed with type 3 advanced sigmoid colon cancer with colonic stenosis and large type 3 gastric cancer in the residual stomach with gross infiltration of the adjacent organs. The patient first underwent sigmoidectomy and then received a regimen of neoadjuvant combination chemotherapy with S-1, cisplatin( CDDP), and Lentinan( LNT)( S-1 80 mg/m2, CDDP 60 mg/m2, and LNT 2 mg/body twice weekly for 2 weeks) for gastric cancer( cT4b[ SI, liver, pancreas], N2M0H0, Stage IIIC). After 2 courses of treatment, the gastric tumor had reduced in size but had penetrated the transverse colon. We performed total resection of the gastric remnant, D2 lymph node dissection, and en bloc resection of the transverse colon, partial liver, pancreas body and tail, partial diaphragm, and pericardium. S-1/CDDP (a total of 11 courses) followed by single-agent S-1 therapy was continued as adjuvant chemotherapy. With a follow-up time of 3 years and 10 months, no recurrence was noted following total resection of the gastric remnant.