Osteoblastic cutaneous osteosarcoma in a cat: combining surgery and electrochemotherapy for local control

Osteosarcoma (OSA) is a mesenchymal tumor originating from osteoblast precursors and is associated with some predisposing factors, including prostheses or metallic implants, areas of bone infarction, and radiation exposure. In cats, this neoplasm exhibits aggressive biological behavior and rapid growth. Extraskeletal OSA is a rare neoplastic disorder arising from stem cells in soft tissues. It is characterized by the proliferation of malignant mesenchymal cells that produce bone matrix or bone tissue without primary involvement of adjacent bone tissue or periosteum. This condition is often linked to previous trauma or chronic inflammation. Here, we present a case report of a 6-year-old, mixed-breed, spayed female cat with a cutaneous nodule located in the interscapular area (1.0x0.7x0.6cm). Clinical examination raised suspicion of feline injection-site sarcoma (FISS), and staging exams revealed no evidence of metastasis. To achieve better local control, the cat underwent surgery with wide margins (5cm lateral margins and two anatomic planes for deep margins), combined with intraoperative electrochemotherapy. Histopathological and immunohistochemical analyses supported the diagnosis of osteoblastic OSA (RUNX2+, S100+, 1A4-, Desmin, MyoD1-, and IBA1-). The patient remains alive and in complete remission (202 days). This case report highlights an innovative treatment for extraskeletal OSA in cats, combining electrochemotherapy with surgical intervention for effective local disease control.