A comprehensive overview of tumour deposits in colorectal cancer: Towards a next TNM classification

The management of colorectal cancer (CRC) highly relies on the TNM staging system. Tumour deposits (TDs), important histoprognostic factors, are detected in approximately 20% of CRCs and associated with poor prognosis. Integration of TDs in the TNM staging remains a subject of lively debate and differs over the successive TNM classifications. Currently TDs, whatever their number, are considered in pathologic staging only in the absence of lymph node metastasis (LNM; subcategory pN1c). However, the medical community is divided over this way of integrating TDs in the TNM staging system. Considering the personalization of the type and duration of adjuvant chemotherapy in stage III colon cancer according to the number of LNM, this issue has become of growing importance. Thus, ignoring TDs in the presence of LNM represents a major prognostic underestimation and leads to wrong therapeutic decisions. Hence, considering the growing significance of prognostic role, the scientific complexity, and a potential therapeutic effect of TDs, we provide an overview of current knowledge about TDs. Based on the results from recent publications, we also provide plausible scenarios of integration of TDs into the next TNM classification system.