Neoadjuvant chemotherapy (NAC) of rectal cancer has some advantages: 1) Whole body control from the early stage of treatment, 2) Tumor reduction (favorable for laparoscopic surgery), 3) No functional failure due to radiation. In this study, a total of 50 patients with rectal cancer, treated with NAC, were examined. The pathological primary cancer area and the radiological cancer volume reduction ratio were measured using CT and/or MRI imaging and the donut-shaped measurement method. Immunostaining of cytokeratin AE1/AE3 was performed to quantitatively measure the cancer cell mass in the largest section of rectal cancer. Cytokeratin AE1/AE3-stained area (P=0.04), mitosis (P=0.0027) and radiological donut-shaped images after NAC (P=0.010) were lower in the high radiological cancer volume reduction ratio group compared with the low radiological cancer volume reduction ratio group.