Background/aims: We analyzed how many lymph nodes should be examined to establish the presence or absence of lymph node metastasis, a staging factor, based on cumulative survival rate in colorectal cancer.
Methodology: Among those who had undergone curative resection of colorectal cancer and lymphadenectomy exceeding D2, 94 patients with Dukes' B colorectal cancer (group B) and 108 patients with Dukes' C colorectal cancer (group C) were investigated, excluding obvious deaths from other diseases. Group B was divided into two groups by the number of lymph nodes examined, and the minimum number of retrieved lymph nodes yielding significant difference in survival rate was determined.
Results: Dividing group B into two groups by the number of lymph nodes examined, survival rate was studied. The minimum number of retrieved lymph nodes yielding significant difference in survival rate between the two groups was observed when group B was divided into one group with 9 or more lymph nodes (72 patients) and the other with less than 9 (22 patients), with cumulative five-year survival rate of 86.7% and 66.7%, respectively. More favorable prognoses were observed in the 9 or more group compared with the less than 9 group or Dukes' C group (p=0.0284, p=0.0032, respectively). On the other hand, survival rate of the less than 9 group was similar to that of the Dukes' C group (p=0.8167).
Conclusions: Based on survival rate, 9 or more lymph nodes should be examined in order to correctly ascertain nodal negativity in lymphadenectomy exceeding D2 for Dukes' B colorectal cancer.