E4922. WHO 2020 Bone Lesion Update: What the Radiologist Needs to Know
  1. Behrang Amini; MD Anderson Cancer Center
Primary bone tumors are a rare and heterogeneous group of neoplasms. The 5th edition of the WHO Classification of Tumors of Soft Tissue and Bone, published in 2020, incorporates advances in understanding of tumor biology and genetics and provides an updated classification scheme for bone tumors. The diversity and morphologic overlap of these tumors with other bone lesions can complicate pathological diagnosis, and radiologists can play a key role in challenging cases. To provide appropriate consultation to pathologists and medical and surgical oncologists, radiologists need to be aware of the classification scheme and important changes since the 4th edition.

Educational Goals / Teaching Points
1) Review the WHO 2020 classification of bone lesions, 2) discuss changes from 2013 that are most relevant to radiologists, and 3) become familiar with imaging features of these entities.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
There has been a change in grading of several lesions (chondroblastoma, chondromyxoid fibroma, synovial chondromatosis, and epithelioid hemangioma). Chondrosarcoma (CS) grade1 and atypical cartilaginous tumor are described as the same pathological entity with a difference in prognosis depending on location, similar to well-differentiated liposarcoma and atypical lipomatous tumor. CS grades 2 and 3 are now in a category by themselves. A new entity, denosumab-treated giant cell tumor has been added, as it can mimic malignancy on histopathology. Chordoma has been split into three entities: conventional chordoma, dedifferentiated chordoma, and poorly differentiated chordoma. Ewing sarcoma has been expanded into a larger category: Undifferentiated small round cell tumors of bone and soft tissue. The non-Ewing entities in this category are primarily differentiated by genetic alterations and have nonspecific imaging features.

An understanding of the changes in the most recent edition of the WHO classification of tumors of soft tissue and bone is necessary for radiologists providing guidance to pathologists and medical and surgical oncologists.