Histological classification of soft tissue tumors and staging according to the TNM system

The classification of soft tissue tumors is based on their resemblance to normal non-neoplastic tissues and provides an indication of how the tumor will behave in the further disease course. The current article presents the principles to be considered when classifying tumors into categories and discusses additional findings to be taken into account in the diagnosis. The importance of considering combinations of findings when classifying a tumor is underscored; individual (in particular immunohistochemical) findings can be misleading. A statement on the grade of malignancy of a soft tissue tumor requires its identification as a known entity, otherwise incorrect prediction of its biological behaviour is possible. The category of "intermediate malignancy" has been added to the categories of "benign" and "malignant", whereby locally aggressive and incidentally metastasizing tumors have been included in this new category. The staging of soft tissue tumors according to the TNM system is explained, emphasizing that one important feature compared with carcinomas is the inclusion of depth localisation and grade of malignancy.