Purpose: Adequate nodal staging of colon cancer has been defined as pathologic examination of at least 12 lymph nodes. We sought to refine this definition by quantifying the likelihood that a pathologically node-negative patient has, indeed, no positive nodes.

Patients and Methods: Patients with stage I-III adenocarcinoma of the colon between 1994 and 2005 and had at least one lymph node pathologically examined were identified from the Surveillance, Epidemiology and End Results (SEER) database (n = 131,953). We estimated the sensitivity of the pathologic staging of locoregional spread using a beta-binomial model and developed the nodal staging score (NSS), which is the probability that a patient is correctly staged as node negative. NSS is a function of T stage and the number of examined nodes.

Results: The probability of missing a positive node that is in fact truly present is 29.7% if five nodes are examined, 20.0% if eight are examined, and drops to 13.6% for 12 nodes are examined. An NSS of 90% can be achieved by examining a single node for T1 and four nodes for T2 tumors. To maintain similar levels of NSS for T3, 13 nodes need to be examined and for T4 lesions, 21 nodes need to be examined. Graphical and tabular tools are provided to facilitate calculation of NSS and treatment decision making in practice.

Conclusion: The minimum number of examined nodes for adequate staging depends on the T stage. The score we developed indicates the adequacy of nodal staging for patients with no positive nodes and can assist clinical decision making in the patient without nodal metastasis.