An 80-year-old man reported at our hospital with the chiefcomplaint ofconstipation. He was diagnosed with sigmoid colon cancer(T4aN0M0, Stage II). He also had steroid-resistant idiopathic thrombocytopenic purpura(ITP)since 2001. After a high dose g-globulin therapy, he underwent sigmoidectomy and splenectomy simultaneously because ofthe steroidresistant ITP. While some reports suggest that ITP is dominant when it occurs with blood cancer, others suggest that it can be immunologically dominant even when it occurs with solid tumors. ITP has a significant effect on solid tumors.