Worst Histology-Based Risk Stratification for Lymph Node Metastasis in Patients With T1b Colorectal Cancer: A Retrospective Pathology-based Study.

Histological subtype is an important pathological factor in risk stratification for lymph node metastasis (LNM) in T1 colorectal cancer (CRC); however, conventional predominant-type assessment may miss minor poorly differentiated components in T1b CRC. We aimed to develop a T1b-specific risk stratification framework incorporating a reproducible worst histology (WH) approach. We retrospectively analyzed 488 patients with pathologically confirmed pT1b CRC who underwent surgical resection with lymph node dissection. Histological evaluation was performed using three approaches: dominant histology (DH), WH, and WH focusing on poorly differentiated adenocarcinoma (WH-por). For each approach, independent risk factors for LNM were identified. Patients without these factors were defined as the low-risk subgroup, and LNM rates were compared with the conventional Japanese Society for Cancer of the Colon and Rectum (JSCCR) criteria. In patients with T1b colon cancer, the WH-por approach demonstrated favorable performance for identifying LNM risk compared with the DH and WH approaches. In contrast, in rectal cancer, the WH approach performed better than the WH-por approach. In the colon cohort, the LNM rate in the low-risk subgroup was 1.7%, compared with 4.1% under the JSCCR criteria. In the rectal cohort, the corresponding rates were 8.0% and 8.6%, respectively. A WH-based approach improves LNM risk stratification in T1b CRC and may help identify carefully selected patients at low risk of LNM, supporting more individualized clinical decision-making, including careful consideration of the necessity of additional surgical resection.Trial Registration: N/A.