Stage II/III cancer of the rectosigmoid junction: an independent tumor type?

The 5-year relapse-free survival rate (5Y-RFS) and 5-year overall survival rate (5Y-OS) were investigated in 766 patients with stage II/III colorectal cancer (CRC). The Stage II group included 283 patients with colon cancer (CC), 40 patients with rectosigmoid junction cancer (RSC), and 74 patients with rectal cancer (RC), while the Stage III group comprised 226 patients with CC, 52 patients with RSC, and 91 patients with RC. Stage III patients with RC were further divided into 68 patients with Ra cancer (Ra, rectum/above the peritoneal reflection) and 23 patients with Rb cancer (Rb, rectum/below the peritoneal reflection). Then the 5Y-RFS and 5Y-OS were calculated for each category or subcategory. The 5Y-RFS/5Y-OS was 80.3/80.6% for Stage II patients and 63.7% (p<0.001)/66.2% (p<0.001) for Stage III patients. In the Stage II group, the survival rates were 82.9/81.2% for CC, 77.6/74.8% for RSC, and 72.9/80.5% for RC, with no significant differences between each category. In the Stage III group, the survival rates were 69.3/72.8% for CC, 71.6/77.7% for RSC, and 46.5/46.2% for RC. There was no significant difference of survival for CC vs. RSC, but significant differences were noted for CC vs. RC (p<0.001/p<0.001) and RSC vs. RC (p=0.008/p=0.007). In the Stage III group, survival rates were 71.6/77.7% for RSC, 47.6/44.8% for Ra, and 45.7/51.3% for Rb, with significant differences for RSC vs. Ra (p=0.013/p=0.005) and RSC vs. Rb (p=0.026/p=0.180), but not for Ra vs. Rb. These results suggest that Stage II/III RS cancer should be classified as colon cancer and should not be considered an independent tumor type.