Background: One of the major changes in the new TNM classification (5th edition, 1997) for gastric cancer was made in the classification of N category: the 5th edition employs the number of involved nodes and a minimum of 15 examined nodes is required for N0 classification. The validity of the new TNM classification was assessed by comparing the survivals according to the number of nodal involvement and especially the cut-off point of number of involved nodes and the problems in N0 classification in T1 were focused.
Patients and methods: Between 1982 and 1999, a total of 641 patients underwent gastrectomy for gastric cancer in our department. The stage and the degree of subcategories were classified according to the pathological assessment after surgery, and the survival and its correlation with clinicopathological factors were statistically analyzed.
Results: pT classification included 325 pT1, 103 pT2, 102 pT3 and 111 pT4 cases, while pN classification included 448 pN-classifiable cases (223 pNO, 149 pN1, 52 pN2 and 24 pN3); 193 were unclassifiable (pNx), 123 of which were classified pNx due to the examined lymph nodes being less than 15. In 448 pTNM-classifiable cases the pN2 and pN3 groups showed almost the same survivals, while the pN1 included subgroups with a significant difference in prognosis. The pN1 category should be classified into two categories: pN1a, 1-3 involved nodes and pN1b, 4-6 involved nodes. Furthermore, out of 325 pT1 cases, 151 (46.5%) were pN-unclassifiable (pNx): 123 were due to the examined number being less than 15 for pN0 classification and 28 where the number of examined nodes were not reported. Although the mean number of examined nodes in pT1 was 24.7 for pN0 and 8.3 for pNx, there were no differences in survival rates between the pT1pN0 group and the pT1pNx group. This suggests the over-requirement of the number of examined nodes for pN0 classification in pT1 cases. We propose that pN0 classification in pT1 should be required for a minimum of 6 examined nodes.
Conclusion: The pN1 category should be subclassified into pN1a and pN1b. Furthermore, pN0 classification in pT1 should be required for a minimum of 6 examined nodes.