Purpose: We have studied 193 cases of colorectal adenocarcinoma from a population-based register to determine the minimum number of lymph nodes to be examined to provide an accurate assessment of the presence of nodal metastases.
Methods: The mean total number of lymph nodes identified per surgical specimen was 11 +/- 6.8 (range, 1-36) using traditional dissection. One hundred eighteen specimens (61 percent) were classified as Dukes B. Seventy-five (39 percent) had lymph node metastases (Dukes C) with a mean of 3.3 +/- 4.7 positive lymph nodes per specimen. With binomial distribution we calculate the probability to find at least one positive node in a sample size n with a determined proportion of positive nodes.
Results: The error probability in the ganglionar assessment by traditional dissection was 0.05 with 6 examined lymph nodes and 0.01 with 10 examined nodes.
Conclusion: We must provide the pathologist with a minimum of six examined lymph nodes per surgical specimen for an optimal Dukes B assessment.