Impact of CRM-oriented specimen processing on lymph node retrieval: a prospective multicenter study evaluating the risk of a suboptimal lymph node yield in rectal cancer.

PURPOSE: This prospective study evaluated the lymph node (LN) yield following CRM-oriented specimen processing, whilw paying particular attention to the proportion of cases with fewer than 12 examined LNs. METHODS: The Kanagawa Yokohama Colorectal Cancer Study Group conducted a multicenter prospective cohort study between 2021 and 2024. Patients with clinical stage II or III lower rectal cancer who underwent surgery without neoadjuvant therapy were enrolled in this study. This study reports a single-arm analysis of the short-term outcomes. Surgical specimens were processed using modified methods that preserved the mesentery adjacent to the tumor. The primary endpoint was the number of retrieved lymph nodes. RESULTS: The median number of retrieved LNs was 19 (range, 2–98), and ≥ 12 LNs were identified in 81.6% of patients. CRM was assessable in 96.1% of the cases. Despite partial preservation of the mesorectum, the LN yield was not inferior to that reported in major clinical trials, and no systematic reduction attributable to the CRM-oriented methods was observed. Exploratory analyses suggested that patients with < 12 examined LNs were more frequently associated with patient- or procedure-related factors. CONCLUSION: CRM-oriented specimen processing enables accurate CRM evaluation, while maintaining LN retrieval within a feasible range and preserving the clinically important threshold of ≥ 12 LNs.