Stage II colonic adenocarcinoma: a detailed study of pT4N0 with emphasis on peritoneal involvement and the role of tumour budding

Aims: Evaluation of peritoneal involvement in colonic cancer (CC) can be difficult. We studied pT4N0 cancers and their association with pathological prognostic markers, including tumour budding. Method and results: Tumours were classified as (i) at the peritoneal surface or free in the peritoneal cavity (pT4a subgroup n = 44); (ii) directly invading adjacent organ (pT4b subgroup n = 8); or (iii) showing inflammatory involvement of the peritoneum (pT4I subgroup n = 25). A published pT3N0 cohort was used to compare Stage II subgroups. Standard pathological markers including tumour budding were assessed. Elastin staining was performed in the pT4I subgroup. Seventy-seven Stage II CCs met inclusion criteria. There was no significant difference in survival across subgroups. pT4b tumours were larger than pT4a tumours (P < 0.001). Over-represented features in pT4a versus pT4b tumours were tumour budding (P = 0.02) and infiltrative margin (P = 0.02). Tumour budding did not predict survival. Using multivariate analysis, neural invasion was the only parameter predictive of survival (hazard ratio = 2.8; 95% CI 1.26.4; P = 0.02). Conclusion: Stage II pT4I CCs have a similar outcome to T4a/b tumours. Elastin staining is useful in defining this group. Tumour budding may facilitate peritoneal invasion in pT4a tumours, but does not predict outcome in pT4N0 disease. Only neural invasion independently predicted poor outcome.