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

Objectives 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. Methods 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. Results 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. Conclusions 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