Tumor Deposits in Colorectal Cancer: Definitions for Ninth Edition of the Tumor Node Metastasis Staging System.

Tumor deposits (TDs) have been a contentious element of the tumor node metastasis staging system for colorectal cancer since their introduction in 1997. Classified within the nodal category, their definition has changed repeatedly due to unclear distinctions from lymph node metastases, extramural vascular invasion, and perineural invasion. Despite updates in the tumor node metastasis system eight edition, ambiguity remains, with current criteria relying heavily on pathologist discretion. The fact that TDs are among the most powerful prognostic indicators warrants standardization, based on scientific evidence. A Delphi consensus among expert pathologists confirmed the lack of specificity and reproducibility in the current definition. In response, a new definition was developed, identifying TDs as discrete tumor nodules in pericolic or perirectal fat, distinct from lymph nodes, extramural vascular invasion, or perineural invasion but possibly originating from them. This definition emphasizes the need to report TDs separately when there is unequivocal tumor extension in relation to vessels or nerves. Size and distance from the primary tumor are debated as potential criteria, although they are not part of the proposed definition. The new definition is a first step to incorporate a more robust, biologically relevant definition of TDs into cancer staging.