Appendicular osteosarcoma in small-breed dogs: 51 cases (1986–2011)

• Autores: Pierre M. Amsellem
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 245, Nº. 2, 2014, págs. 203-210
• Idioma: inglés
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• Resumen

  • Objective—To describe outcomes for small-breed dogs with appendicular osteosarcoma.

    Design—Multi-institutional retrospective case series.

    Animals—51 small-breed dogs.

    Procedures—Records from participating Veterinary Society of Surgical Oncology members were searched for dogs that weighed ≤ 15 kg (33 lb) with a histologic diagnosis of appendicular osteosarcoma. The Kaplan-Meier method was used to determine median survival times (MSTs), and Cox regression was performed to identify variables associated with survival time.

    Results—Tumors were most commonly located on the humerus (n = 15) and femur (14). Of the 51 study dogs, 9 were treated nonsurgically, 16 underwent amputation of the affected limb only, and 26 underwent curative-intent treatment, with MSTs of 112, 257, and 415 days, respectively. The MST did not differ significantly between dogs in the amputation-only and curative-intent groups. For dogs in the nonsurgical group, MST decreased significantly as the tumor histologic score increased. For dogs in the amputation-only group, MST decreased as body weight increased.

    Conclusions and Clinical Relevance—For the small-breed dogs with appendicular osteosarcoma of the present study, tumor histologic grade and mitotic index were subjectively lower and MST following amputation of the affected limb without adjuvant chemotherapy was longer, compared with those for similarly affected larger dogs. Results indicated no significant advantage in MST for dogs that underwent curative-intent treatment versus dogs that underwent amputation only, and further investigation of the importance of adjuvant chemotherapy is warranted.

    Appendicular osteosarcoma is the most common primary bone tumor in dogs.1 Curative-intent treatment options typically consist of a combination of local disease treatment (amputation, limb-sparing surgery, or stereotactic radiosurgery) and chemotherapy.2 A survival time of approximately 12 months is expected for affected dogs following the combination of local disease treatment and chemotherapy because metastatic disease generally develops.3,4 Osteosarcoma primarily affects large-breed dogs. In a study5 of 162 dogs with appendicular osteosarcoma, all dogs weighed > 20 kg (44 lb). In a reviewa of 1,462 dogs with osteosarcoma, only 73 (5%) weighed < 13.6 kg (30 lb). Osteosarcoma has a different skeletal distribution in small-breed dogs, compared with that in large-breed dogs. Results of a study6 of dogs with osteosarcoma indicate that the tumor was located on the appendicular skeleton of approximately 47% (29/61) of small dogs (≤ 15 kg [33 lb]) and 82% (61/74) of large dogs (≥ 25 kg [55 lb]). For small-breed dogs, the most common appendicular sites for the development of osteosarcomas are the distal aspect of the tibia, distal aspect of the radius, proximal aspect of the tibia, and femur6–8; however, the number of small-breed dogs with appendicular osteosarcoma is too small to make any conclusions regarding predilection sites for tumor development. Results of 2 studies7,8 indicate an association between multiple bone infarcts and osteosarcoma in small-breed dogs and suggest that the pathogenesis of osteosarcoma could differ between small-breed and large-breed dogs. To date, the literature6,7,9,10 contains information on the treatment and outcome for only 16 dogs < 15 kg with osteosarcoma. In 1 study,6 2 dogs were treated with a combination of amputation and an investigational drug; both developed pulmonary metastases and survived 17 and 51 weeks. In a case series7 of 6 small-breed dogs (3 of which were Miniature Schnauzers) that had bone infarcts and osteosarcoma, the affected limb was amputated in 5 dogs and the remaining dog was euthanized at the time osteosarcoma was diagnosed and had evidence of pulmonary metastases detected during necropsy. Of the 5 dogs in that study7 that underwent limb amputation, 1 was administered adjuvant chemotherapy consisting of high-dose methotrexate and leucovorin rescue and survived 7 weeks, 2 survived 19 weeks, and the remaining 2 dogs were still alive at 40 and 68 weeks after osteosarcoma diagnosis. The 3 dogs that died after treatment all had pulmonary metastases evident during necropsy.6 In another study,9 a terrier with osteosarcoma of the calcaneus survived > 4 years after diagnosis but the treatment was not described in detail. In yet another study,10 2 small-breed dogs with appendicular osteosarcoma that underwent limb amputation only developed metastases and were euthanized or died 2 and 6 months after surgery.10 Overall, the literature6,7 describes only 3 small-breed dogs with appendicular osteosarcoma that were administered curative-intent treatment, which makes it difficult to draw any conclusions regarding the prognosis for such dogs. Specifically, tumor predilection sites, tumor histologic grade, MST, and factors that affect survival time and DFI remain unknown for small-breed dogs with appendicular osteosarcoma.

    The objectives of the study reported here were to describe the signalment; clinical signs; physical examination, radiographic, laboratory, and histologic findings; and incidence and pattern of metastasis at initial evaluation for small-breed dogs (≤ 15 kg) with appendicular osteosarcoma. Additional objectives were to describe treatments, time to development of metastases, and survival times for those dogs that subsequently underwent treatment and evaluate factors such as age, sex, pretreatment total serum ALP activity, primary tumor location, tumor stage and histopathologic grade, and adjuvant treatments as prognostic indicators for survival.