Telangiectatic osteosarcoma in the dog.

Abstract

Osteosarcoma is a malignant neoplasm of bone that contains at least a sarcomatous stroma and tumor osteoid. It may contain various quantities of neoplastic fibrous connective tissue, cartilage, and bone as well. Histologic classifications of this tumor are based on the proportions of these components. The three most common histologic types are osteoblastic, fibroblastic and chondroblastic [l, 2,4]. A rare variant described in both man and dog is the telangiectatic osteosarcoma, also called “malignant bone aneurysm” in some earlier literature [l, 2,4,5]. It is composed of large bloodfilled spaces lined by malignant osteoblasts that produce a minimum of osteoid. Mitotic figures are numerous, but other components of blastic osteosarcomas such as cartilage and bone are absent. Radiographs show a lytic lesion with no appreciable sclerosis [2, 31. A special consideration of this tumor is warranted from two standpoints: differential diagnosis and prognosis. Primary hemangiosarcoma of bone is well recognized [4,6], and must be differentiated from osteosarcoma. The presence of vascular spaces lined only by endothelial cells and the absence of osteoid in the hemangiosarcoma are the key histologic features used to differentiate hemangiosarcoma from telangiectatic osteosarcoma. A recent review of 25 selected cases of telangiectatic osteosarcoma in man led to the conclusion that the prognosis with this variant is bleaker than with other types of osteosarcomas [3]. It has been described as inevitably fatal in the dog [5]. Dog 1, an 8-year-old female German Shepherd, had right shoulder and foreleg lameness and a subcutaneous mass in the dorsum of the neck. A skeletal radiologic survey showed a normal thorax and an osteolytic lesion of the right scapula (fig. I). Many neutrophils in the neck mass and highly undifferentiated neoplastic cells with a few multinucleated giant cells in the scapular lesion were seen in Giemsa-stained smears of needle aspirates. The preliminary diagnoses were an abscess in the neck and undifferentiated sarcoma in the scapula. A fleshy mass with a necrotic center and a portion of the scapulo-humeral joint capsule were removed surgically and the dog was placed on a regime of chemotherapeutic drugs, Adriamycin (Doxorubicin, Adria Labs, Wilmington, Del.) and DTIC (Dacarbazine, Dome Labs, West Haven, COM.). Histologic examination showed a highly vascular mass with large and small vascular spaces lined by large neoplastic cells and masses of large anaplastic malignant cells with numerous mitotic figures (fig. 2, 3). Necrosis, hemorrhage, multinucleated cells, and some fibrosis were seen. The original diagnosis was hemangiosarcoma, but this diagnosis was changed to telangiectatic osteosarcoma when osteoid (fig. 3) was found at reexamination. The dog did not respond to chemotherapy, and was killed. At necropsy, a bloody friable 9 X 8-cm mass was found in the right scapula and the head of the humerus. Histologic examination showed the same changes as described above and confirmed the diagnosis of telangiectatic osteosarcoma.