Novel risk factors for lymph node metastasis in early invasive colorectal cancer: a multi-institution pathology review

Background Novel risk factors for lymph node metastasis (LNM) in T1 colorectal cancer (CRC) have been recently proposed, but most have not been implemented because of the lack of validation. Here we determined the value of poorly differentiated clusters (PDCs) in a multi-institutional cohort of T1 CRC cases. Methods A pathology review involving 30 institutions was conducted for 3556 T1 CRCs. PDC was defined as malignant clusters comprising >= 5 cells and lacking a glandular formation. The ability to identify LNM risk was compared using Akaike's information criterion (AIC). Results PDC was observed in 1401 tumors (39.4 %), including 94 (17.8 %) with <1000 mu m submucosal invasion and 1307 (43.2 %) with >= 1000 mu m submucosal invasion (P<0.0001). The incidence of LNM was higher in PDC-positive tumors (17.4 %) than in PDC-negative tumors (6.9 %; P<0.0001), and PDCs had an adverse impact on LNM irrespective of the degree of submucosal invasion. Grade 3, vascular invasion, budding, and submucosal invasion depth were also significant factors (all, P<0.0001). AIC of risk factor to identify LNM risk was most favorable for vascular invasion (2273.4), followed by PDC (2357.4); submucosal invasion depth (2429.1) was the most unfavorable. Interinstitutional judgment disparities were smaller in PDC (kappa, 0.51) than vascular invasion (0.33) or tumor grade (0.48). Conclusions PDC is a promising new parameter with good ability to identify LNM risk. Use of its appropriate judgment criteria will enable us determine whether an observational policy can be safely applied following local tumor excision in T1 CRC cases.