Reconsidering the prognostic significance of tumour deposit count in the TNM staging system for colorectal cancer

Although the occurrence of tumour deposits (TDs) without metastatic lymph nodes (mLNs) is classified as “N1c” in the 8(th) TNM staging system for colorectal cancer (CRC), the prognostic significance of the TD count is still controversial. A total of 39155 CRC patients were collected from the Surveillance, Epidemiology, and End Results (SEER) database. The potential associations between baseline characteristics and TD status were evaluated using the χ(2) test. Cancer-specific survival (CSS) rates were calculated by using the Kaplan-Meier method, and CSS comparisons were performed by using the log-rank test. The results showed that TD count was an important prognostic factor and that the number of TDs was negatively correlated with the prognosis of CRC patients. We found that the prognostic value of one TD is equivalent to that of two mLNs based on the comparison of CSS rates. Accordingly, we proposed a novel N staging system by integrating the TD count into the N category with the ratio of TDs to mLNs being 1:2. There were no prognostic differences in patients with or without TDs in each novel N category. Weighing one TD as two mLNs in this novel TNM staging system is superior to the “N1c” classification in the 8(th) TNM staging system in evaluating the prognosis of CRC patients.