Extraskeletal osteosarcoma and its histological mimics

•EOS contains bone but other sarcomas may rarely produce bone and thus histologically mimic EOS.•Benign lesions producing immature bone and cartilage may histologically mimic EOS on core needle biopsy.•EOS with focal bone formation may require extensive sampling, IHC and sequencing for correct diagnosis.•MDM2 and CDK4 amplifications may occur in EOS but do not correlate with improved prognosis.•Best chemotherapy for treating EOE is controversial with conclusions hampered by lack of prospective data.