Tumour budding is associated with the mesenchymal colon cancer subtype and RAS/RAF mutations: a study of 1320 colorectal cancers with Consensus Molecular Subgroup (CMS) data

Tumour budding is an important prognostic factor in colorectal cancer (CRC). Molecular profiling of tumour buds suggests (partial) epithelial–mesenchymal transition and cancer stem-cell phenotype, similarly described in the “mesenchymal” Consensus Molecular Subtype 4 (CMS4), which identifies a particularly poor prognostic subgroup. Here, we determine the association of tumour budding with CMS classification, prognosis, and response to therapy. AMC-AJCCII-90 cohort (n = 76, stage II) was evaluated for peritumoural budding on H&E slides. LUMC (n = 270, stage I–IV), CAIRO (n = 504, metastatic CRC) and CAIRO2 (n = 472, metastatic CRC) cohorts were investigated for intratumoural budding using pan-cytokeratin-stained tissue microarrays. Budding was scored as count/area, then classified as <5 or ≥5 buds. For all cohorts, CMS classifications were available (gene-expression/immunohistochemistry-based classifiers). High (≥5) budding predicted a worse outcome in multivariate analysis in AMC-AJCCII-90 (p = 0.018), LUMC (p < 0.0001), and CAIRO (p = 0.03), and in CAIRO2 (continuous variable, p = 0.02). Tumour budding counts were higher in CMS4 compared to epithelial CMS2/3 cancers (p < 0.01, all), and associated with KRAS/BRAF mutations (p < 0.01, AMC-AJCCII-90, CAIRO, CAIRO2). Tumour budding is an adverse prognostic factor across all CRC stages and is associated with the mesenchymal CMS4 phenotype. KRAS/BRAF mutations are strongly correlated with tumour budding suggesting their involvement in the regulation of this process.