As with conventional radiation therapy, pathologic fracture may occur after treatment since the quality of the bone structure is often compromised by tumor-associated osteolysis. The limiting factors of stereotactic radiosurgery therapy for appendicular osteosarcoma are the size of the tumor and the condition of the bone at the time of therapy, as adequate coverage of large tumors with the 30-Gy isodose line is not always possible and the risk of pathologic fracture remains after treatment. The use of external coaptation to decrease this risk has not been evaluated. Thus, stereotactic radiosurgery should ideally be used to treat appendicular osteosarcomas that are relatively small and have caused minimal bone destruction.

An additional limb-sparing technique that uses intraoperative radiotherapy has been used in a small number of dogs with osteosarcoma located at sites other than the distal radius or ulna.¹ After surgically isolating the tumor from the surrounding soft tissues, the surgeon performs an osteotomy through an unaffected portion of the bone proximal or distal to the tumor site. While maintaining joint capsule attachments, the surgeon then rotates the neoplastic bone segment out of the surgical field, and a single dose of 70 Gy is delivered to the neoplastic bone segment. The irradiated bone segment is replaced in situ, and the osteotomy is stabilized with internal fixation.¹

CHEMOTHERAPY

TABLE 1 Median Survival Times for Appendicular Canine Osteosarcoma.

Using cisplatin or doxorubicin as a single agent as adjunctive treatment to amputation has yielded median survival times ranging from 262 days⁵⁰ to 366 days,⁵¹ one-year survival rates ranging from 37%^50,54 to 46%,⁴¹ and two-year survival rates ranging from 16%⁵⁰ to 26%.⁵⁴ These results show a significant improvement in survival over amputation alone, which has been reported to yield a median survival time of 102 to 175 days, a one-year survival rate of 12%, and a two-year survival rate of 2%.^8,49,54 Carboplatin is an alternative chemotherapeutic agent that is at least as efficacious as cisplatin.⁵⁶ Carboplatin is a second-generation platinum compound that, unlike cisplatin, does not induce nephrotoxicity and is easier to administer. Although initially some combination protocols (e.g. cisplatin and doxorubicin) appeared to offer survival benefit over single-agent therapy,⁶⁰ recent evidence indicates that combination protocols do not increase survival.^55,57,58

Other chemotherapeutic agents that have been evaluated for treating canine osteosarcoma in combination with amputation and limb salvage include cisplatin-impregnated open-cell polylactic acid polymer (OPLA-Pt) and liposome-encapsulated muramyl tripeptide-phosphatidylethanolamine (liposome/MTP-PE).^61,62 Cisplatin-impregnated OPLA-Pt has been placed in the wound bed adjacent to allografts in limb salvage cases to reduce local tumor recurrence and has been reported to reduce local recurrence by 10%.⁶¹ Liposome/MTP-PE has also been shown to be effective in treating dogs with osteosarcoma.⁶² In one study, dogs treated by amputation and intravenous liposome/MTP-PE had a median survival time of 222 days, while those treated with empty liposomes had a median survival time of only 77 days.⁶² Aside from mild elevations in body temperature (1.8 to 3.6 F [1 to 2 C]) for two to six hours after injection, treatment with liposome/MTP-PE was well-tolerated.

Chemotherapy has also been evaluated in dogs with measurable pulmonary metastatic osteosarcoma.⁶³ Single-agent therapy with either cisplatin, doxorubicin, or mitoxantrone was ineffective in treating measurable metastatic disease, providing a median survival time of only 61 days (range, 14 to 192 days).⁶³