%0 Journal Article %T Bone and soft tissue tumors at the borderlands of malignancy. %A Crim J %A Layfield LJ %J Skeletal Radiol %V 52 %N 3 %D Mar 2023 %M 35767018 %F 2.128 %R 10.1007/s00256-022-04099-1 %X This review examines findings of musculoskeletal neoplasms whose equivocal imaging and/or histopathologic features make it difficult to determine if they will show aggressive behavior. We include both intermediate tumors as defined by the World Health Organization (WHO), and a single low-grade malignancy, low-grade central osteosarcoma, which mimics a benign lesion on imaging and histology. Intermediate tumors are a broad category and are subdivided into tumors that have risk of local recurrence only, and ones that have a risk of distant limb and pulmonary metastases. Difficult intermediate musculoskeletal lesions include atypical cartilaginous tumor/grade 1 chondrosarcoma, atypical lipomatous tumor/grade 1 liposarcoma, and solitary fibrous tumor. We review diagnostic criteria, differential diagnosis, and recommendations for surveillance.