Ultrasonography of Osteosarcoma in Dogs
Sonography Atlas of Dogs

Since its clinical introduction, CT has revolutionized veterinary medicine. This technique is considered to one of the most valuable tools for the imaging work-up of neurological, oncological and orthopedic canine or feline patients ¹⁹. The CT is useful for detecting the presence of any soft tissue mass adhered to the cortex or in the medullary canal, cortex thickening, cortical scalloping, and any periosteal reaction perpendicular to diaphysis and extending into the soft tissue mass ^{20, 14}.

CT has been used to investigate primary osteosarcoma lesions, pulmonary metastatic disease, and bone metastases identified on bone scan ²¹. CT is also used for evaluation of calcification and homogeneity of the non-mineralized component of soft tissue mass ¹⁴.

Differential diagnosis of periosteal osteosarcoma is important to elucidate the nature of osteosarcoma ¹⁴. In general, histopathological and morphological findings mingle and may lead to a misleading classification of osteosarcoma. The round cell tumors may be present as a spiculated lesion in the cortical bone. The differential diagnosis should include the other types of osteosarcoma (parosteal osteosarcoma, central osteosarcoma, high-grade surface osteosarcoma and chondroblastic osteosarcoma) ⁴. Equally important, the guidance for the differential diagnosis of periosteal osteosarcoma can be performed by radiographic characteristics, as well as by clinical significance ¹⁴.

In humans, before the surgery, it is essential to establish whether the tumor involves the medullary canal and CT provides this information. If the medullary canal is involved the tumor should be treated like a classical central osteosarcoma or chondrosarcoma ¹⁵.

As well as in humans, adequate surgical treatment seems to be essential for tumor control. Limb amputation or limb-sparing surgery is the first method of treatment ². Limb-sparing surgery is an alternative method to limb amputation ^{15, 2} and this technique is recommended for dogs with compromising neurologic or orthopedic problems ²². This method can be beneficial for owners who refuse to perform limb amputation ²². Moreover, tumor recurrence appears in 15–25 % of cases. If surgical treatment is timely and adequate, the survival rate is increased and metastasis is significantly reduced ¹⁴.

In humans, the prognosis of periosteal osteosarcoma is based on several factors. These include the anatomical position of the tumor, the degree of invasion into the cortex or medulla, and the histopathological grade. Some studies have shown that the anatomical position could influence survival time. This trend was extrapolated to patients with periosteal osteosarcoma. However, according to the results of this study, the anatomical position did not influence the survival rate ^{15, 14}. The number of periosteal osteosarcoma cases reported in dogs is insufficient to determine the prognosis ¹⁷.

In all types of osteosarcoma, adjuvant chemotherapy may be performed to provide pharmacological support following the surgical procedure. Manifold studies have been performed to assess if the survival time of dogs with osteosarcoma can be prolonged by adjuvant therapy ²³. Latest reports showed the efficiency of few chemotherapeutic drugs. The adjuvant chemotherapeutic protocols include the use of cisplatin, carboplatin, and doxorubicin. However, the outcome remains inconclusive ². Chemotherapy is usually indicated for patients with osteosarcoma, but the advantages are still uncertain ¹⁴.

In a veterinarian study, a comparison of the median survival time of 48 dogs with appendicular osteosarcoma after receiving single-agent carboplatin (300 mg/ m (2) IV q 21 days for 4 cycles) were performed after the following amputation to amputation alone. Dogs treated with adjuvant therapy had a prolonged median survival time (307 days) in comparison to those after surgery alone (138 days) ^{24, 25, 2}.

Some authors indicated significantly longer median survival time for dogs with appendicular osteosarcoma treated with adjuvant chemotherapy with cisplatin followed by amputation or limb-sparing surgery (322 days) than with surgery alone (138 days) ^{26, 27}. The results indicated the effectiveness of the treatment with cisplatin, but it did not inhibit metastases ².

The use of doxorubicin in osteosarcoma’s treatment is considered as effective as cisplatin or carboplatin. Doxorubicin demonstrated efficacy in slowing down metastasis in dogs with appendicular osteosarcoma with one, two, and three-year median survival time of 35%, 17%, and 9% respectively ²⁸. These results were similar to those with carboplatin as the adjuvant method, which indicates that both drugs might be used to prolong patients’ lives; however, neither of them inhibits metastasis ².

Alternative chemotherapy protocols for osteosarcomas include using lobaplatin or ifosfamide. The protocol with ifosfamide was evaluated in dogs with osteosarcoma and previously managed with standard chemotherapy. The findings indicated that ifosfamide was well tolerated but had lower anti-tumor activity ²⁹. Promising results showed the efficiency of lobaplatin on the group of 28 dogs with osteosarcoma ³⁰. Compared to dogs used as controls treated only with surgery alone, the results suggest that lobaplatin prolonged the disease-free interval and survival time in dogs with osteosarcoma. More than 20 % of dogs reached one-year disease-free interval and more than 30 % of dogs reached one-year survival time ^{31, 2}.

Another way to improve the efficacy of chemotherapy was comparing the effects of two different antineoplastic drugs administered on the alternative way. The alternating efficiency of administration of cisplatin and doxorubicin after amputation was evaluated in a study. Thirty-eight dogs treated with combination therapy after amputation had significantly longer survival free time than dogs treated with isolated amputation, but this result was similar to that obtained during monotherapy involving carboplatin or doxorubicin ^{31, 32, 33}. These results demonstrated that the combination of the two drugs did not increase the free survival time compared to monotherapy. However, lower adverse effects were observed in these patients ². On the other hand, dogs with appendicular osteosarcoma receiving carboplatin alone had significantly longer disease-free intervals than dogs receiving carboplatin and doxorubicin in an alternate scheme ²³. In summary, there is no clear evidence that combined chemotherapy is more effective than single-agent therapy; however, it may reduce adverse effects, which may indicate that the use of multidrug in a long-term therapy increases the quality of life ².

The clinical evidence based on the biological behavior of osteosarcomas suggested that the first choice of treatment for periosteal osteosarcoma should be surgery. The recommendation of chemotherapy protocols after surgery remains unclear since complete remission and the occurrence of metastases cannot be warranted. In veterinary medicine, the information is scarce for this type of osteosarcoma. Most of them come from human case reports. Therefore, a study involving periosteal osteosarcoma in dogs should be stimulated to obtain more information about the incidence, biological behavior, tumor site, prognosis and free survival time.