Background: National guidelines define adequate lymph node (LN) sampling in colon cancer (CC) as 􀀪 12 LNs. Recent data suggests that sidedness impacts survival in CC. The difference in LN number to accurately stage

T3N0 disease in right vs left CC has not been previously evaluated in a prospective trial.

Methods: Patients with pathologic T3 CC who had at least one LN examined were identified from a randomized, multicenter, international trial of ultrastaging in CC (ID: NCT00949312). The probability of true nodal negativity based on the number of LNs examined was calculated for left and right CC. These results were then validated in a cohort of patients with similar inclusion criteria selected from the National Cancer Database (NCDB) between 2006 and 2014. Results: 370 patients met the inclusion criteria in the trial cohort; 48% were LN-negative. Of 153,945 patients in the NCDB with similar inclusion criteria, 57% were LN-negative. The probability of true nodal negativity when 12 LNs were examined was 64% for left and 68% for right CC in the trial cohort and 72% and 77% in the NCDB. The probability (80-95%) of true nodal negativity comparing left to right CC was significantly different in both the trial (p <0.001) and the NCDB (p <0.001) (Table 1).

Conclusions: In both a prospective multicenter trial and the NCDB, sidedness influences the total number of LNs needed to predict nodal negativity in CC. Current guidelines regarding the minimum number of LNs needed to accurately stage patients with T3N0 CC may need to be re-evaluated since the decision to treat patients with adjuvant chemotherapy is largely determined by LN status.