Tumor deposits are encountered in advanced colorectal cancer and other adenocarcinomas: an expanded classification with implications for colorectal cancer staging system including a unifying concept of in-transit metastases.

The seventh edition of the TNM Classification of Malignant Tumors is due to be published soon. In the current version dating back to 2002, tumor deposits, which are metastatic lesions commonly encountered in the routine histopathological examination of advanced colorectal cancer specimens, are classified according to their shape with different implications for staging. So distinguished, these lesions are considered either as metastatic lymph nodes (N category) or as vascular invasions (T category). We recently proposed a more comprehensive classification approach that also includes the M category. Relying on two of our independent recent studies, we aim here to provide suggestions for a novel classification of tumor deposits with diverse implications for TNM staging system of colorectal cancer. Furthermore, we show that tumor deposits are not limited to colorectal cancer, but they are common to different adenocarcinoma types.