Important role of tumor deposits and negative lymph nodes in prognosis of N1c colorectal cancer patients.

Background: The number of tumor deposits (TDs) does not play a part in the current tumor node metastasis staging. Negative lymph node (NLN) status is associated with the prognosis of colorectal cancer (CRC), but its clear role in N1c stage remains to be defined.

Aim: To evaluate the combination of TDs and NLNs as potential prognostic indicators in N1c CRC.

Methods: We retrospectively identified 107 consecutive patients who had N1c CRC radically resected at China-Japan Friendship Hospital. The combination of TDs and NLNs was calculated by the formula NLNTD = NLN/(TD + 1). Cutoff values of NLNs and NLNTD were determined using the R package "survminer". Disease-free survival (DFS), overall survival (OS) and cancer-specific survival (CSS) were determined using the Kaplan-Meier method to assess the impact of NLNTD on prognosis. Results were compared using the log-rank test.

Results: The median follow-up time was 63.17 (45.33-81.37) months for DFS, with 33.64% (36/107) of patients experiencing recurrence during follow-up. Five-year DFS was 66.0% (57.3%-76.0%). There was no significant difference in prognosis between patients with > 12 and ≤ 12 NLNs (P = 0.058) for DFS. Similar results were seen according to the number of TDs. The definition of NLNTD = NLN/(TD + 1) with a cutoff value of 6 divided patients into two groups with different DFS (P = 0.005). Five-year DFS for patients with NLNTD > 6 was 73.5% (63.6%-85.0%), compared with 50.0% (35.7%-70.0%) for those with NLNTD ≤ 6. These two groups had different prognosis without perineural invasion (P = 0.012) or lymphovascular invasion (P = 0.002) even neither (P = 0.053). Similar results were seen for OS and CSS.

Conclusion: NLNTD could serve as important prognostic factor for outcomes in N1c CRC patients. These patients could be stratified for prognosis through NLNTD and the high-risk should be given more attention during treatment.