Prognostic and predictive values of tumour budding in stage IV colorectal cancer

Background Tumour budding is an important prognostic feature in early‐stage colorectal cancer, but its prognostic significance in metastatic disease has not been fully investigated. Methods Patients with stage IV disease who had primary colorectal tumour resection without previous chemotherapy or radiotherapy from January 2000 to December 2018 were reviewed retrospectively. Budding was evaluated at the primary site and graded according to the criteria of the International Tumor Budding Consensus Conference (ITBCC) (BD1, low; BD2, intermediate; BD3, high). Patients were categorized by metastatic (M1a, M1b) and resectional (R0/R1, R2/unresected) status. Subgroups were compared for overall (OS) and recurrence‐free (RFS) survival in R0/R1 subgroups; R2/unresected patients were evaluated for the rate of tumour progression, based on change in tumour size from baseline. Results Of 371 patients observed during the study, 362 were analysed. Patients with BD3 had a lower 5‐year OS rate than those with BD1 + BD2 (18·4 versus 40·5 per cent; P