Quantitative Histology of Nonmetastatic Regional Lymph Nodes as a Novel Prognostic Indicator in Microsatellite...

Regional lymph node metastasis is one of the main factors affecting cancer staging. However, the clinical and immunologic implications of nonmetastatic regional lymph nodes (nrLNs) remain poorly understood. Here, we investigated the prognostic significance of the morphologic features of nrLNs in colorectal cancer (CRC) with microsatellite instability-high (MSI-H). Artificial intelligence-aided digital pathology-based quantification of 37 histologic parameters in 873 whole-slide images comprising 5785 nrLNs was performed in 2 independent cohorts of curatively resected MSI-H CRCs (discovery, n = 103; validation, n = 90). The prognostic value of each histologic parameter was evaluated by univariate and multivariate disease-free survival analyses. Quantitative immunohistochemical analysis of tumor-infiltrating immune cells and whole-exome and transcriptome sequencing using tumor tissues were performed to assess associations between prognostic nrLN histologic features and various tumor immuno-molecular factors. As a result, germinal center (GC)-related histologic parameters, including the maximum area, mean area, sum area, and maximum diameter of GCs in the nrLNs, were identified as independent prognostic factors in both cohorts. The prognostic GC-related factors of nrLNs were significantly associated with tertiary lymphoid structures and B cell pathways activation but were not or inversely correlated with the densities of tumor-infiltrating T cells and macrophages. No significant associations were found between prognostic nrLN GC features and major tumor molecular factors such as tumor mutational burden, driver mutations, consensus molecular subtype, or CpG island methylator phenotype. In conclusion, quantitative GC-related histology of nrLNs can serve as a prognostic indicator for MSI-H CRC. Our findings suggest that GC-activated nrLNs may represent B cell-mediated antitumor immunity, independent of tumor-infiltrating T cells and tumor-intrinsic molecular characteristics.