The number of metastatic lymph nodes exhibiting poorly differentiated clusters predicts survival in patients with pStage III colorectal cancer

PURPOSE: Many studies have proposed alternative designations for lymph node (LN) status in colorectal cancer (CRC); however, knowledge of histopathological features in metastatic lymph nodes (MLNs) is limited. This study investigated the clinicopathological significance of poorly differentiated clusters (PDCs) in MLNs. METHODS: Slides from 159 patients with pathological Stage III CRC were reviewed. Those with <12 dissected LNs (DLNs) were ineligible. PDCs composed of ≥5 cancer cells lacking full glandular formation and ≥10 PDCs under ×20 objective lens were defined as positive, and the number of MLNs with positive PDCs (MLNs-PDCs) was counted. Results were correlated with patient survival and comparisons made with other indications of LN status. RESULTS: The mean numbers of MLNs and MLNs-PDCs were 2.8 and 1.0, respectively, and were moderately and positively correlated with each other. Univariate analysis identified cutoffs of ≥5 MLNs (86 vs. 55 %, p = 0.024), ≥2 MLNs-PDCs (85 vs. 63 %, p = 0.008), and ≥30 % LN ratio (85 vs. 44 %, p = 0.036) to indicate a positive LN status. However, no cutoff for DLNs was obtained. MLNs-PDCs (≥2) were associated with pT4 tumor (p = 0.0035), open surgery (p = 0.016), greater number of MLNs (p < 0.0001), and positive-PDC primary tumor (p < 0.0001). In multivariate analysis, a prognostic model incorporating ≥2 MLNs-PDCs provided the lowest Akaike information criterion value; consequently, both pT4 tumors (p < 0.001) and ≥2 MLNs-PDCs (p = 0.038) were revealed to be significant prognosticators. CONCLUSION: Results showed that applying the number of MLNs-PDCs could improve stratification in pStage III CRC and may be a valuable candidate for LN status.