Mandibular Osteosarcoma Mimicking Bisphosphonate-associated Osteonecrosis on 99m Tc-MDP Bone Scan in a Patient With Breast Cancer.

We present the case of a 27-year-old woman with a history of left breast invasive ductal carcinoma who developed mandibular osteosarcoma, as documented by 2 MDP bone scans. She had undergone a radical mastectomy, chemotherapy, radiotherapy, and intravenous zoledronic acid therapy. An initial bone scan 1 year later showed increased MDP uptake in the right mandible, suggesting drug-related osteonecrosis, but concurrent CT scans were normal. A follow-up bone scan performed 16 months later demonstrated increased MDP uptake in both mandibles. Subsequent partial mandibulectomy confirmed conventional osteosarcoma.