Is the T1/2N1 (≤3 nodes) category actually stage IIIA (TNM)/IIIa (Japanese classification) in patients with primary colorectal cancer?

The 5-year relapse-free survival rate (5Y-RFS) and the 5-year overall survival rate (5Y-OS) were calculated for 972 patients (stage I, 206 patients; stage II, 396 patients; stage III, 370 patients). We divided the stage III group into 259 patients with IIIa/N1 disease (≤3 positive nodes) and 111 patients with IIIb/N2 disease (≥4 positive nodes) according to the Japanese classification. The IIIa/N1 and IIIb/N2 categories were each subdivided into T1/2 (stage IIIa, 45 cases; IIIb, 9 cases) and ≥T3 (stage IIIa, 214 cases; IIIb, 102 cases) according to the TNM classification, and 5Y-RFS and 5Y-OS were compared between each subcategory and each group. The 5Y-RFS/5Y-OS values calculated for each stage were as follows: stage I, 94.0/90.7%; stage II, 80.5/81.1%; stage III, 63.5/65.7%. When stage IIIa was compared with IIIb, we obtained 67.9/72.0% for stage IIIa and 53.6% (p=0.001)/50.4% (p<0.001) for stage IIIb. For stage IIIa vs. IIIb in the ≥T3 category, we obtained 63.1/68.5% for stage IIIa and 51.9% (p=0.010)/49.0% (p=0.008) for stage IIIb. For stage IIIa vs. IIIb in the T1/2 category, we obtained 92.1/92.0% for stage IIIa and 72.9% (p=0.040)/63.5% (p=0.003) for stage IIIb. There were significant differences between T1/2 and ≥T3 within stage IIIa (p=0.001/p=0.009), but not within stage IIIb. These results suggest that the T1/2N1 category of colorectal cancer should be classified as a subcategory of stage IB/Ib rather than stage IIIA (TNM)/IIIa (Japanese classification).