Page 1393 - Clinical Small Animal Internal Medicine

150 Tumors of Bone and Joint 1331

distal radius. The presence of a pathologic fracture is appendicular OSA in the dog is assumed to be metastatic
VetBooks.ir considered a relative contraindication for limb‐sparing, at the time of diagnosis. The extremely high likelihood of
microscopic metastases is supported by studies evaluat-
as fracture may predispose to spread of tumor cells and
subsequent local recurrence. Significant complications
In dogs with OSA that receive amputation alone, the
associated with limb‐sparing surgery include infection, ing survival of dogs undergoing amputation alone.
implant failure, and local recurrence. Infection rates one‐ and two‐year survival rates are only 11.5% and 2%
associated with limb‐sparing surgery are high, and have respectively. Systemic therapy to control the outgrowth
been described as ranging between 30% and 70%. This of micrometastasis is therefore recommended.
high rate of infection is likely due to a variety of factors Many chemotherapy drugs and combination protocols
such as impaired vascular supply, minimal soft tissue have been attempted, but a clear benefit of any one par-
coverage, implants, and subsequent delivery of chemo- ticular protocol has not been clearly documented; pre-
therapeutics. Infection, however, has been associated ferred protocols often vary by doctor or institution. In
with a prolonged survival time compared to dogs that do general, chemotherapy with single‐agent carboplatin,
not experience infection; dogs with surgical site infection doxorubicin or alternating carboplatin and doxorubicin
have been shown to have median survival times approxi- seems currently most favored and generally results in
mately twice as long (an average of 250 days longer) as median survival times of 8–12 months. In the authors’
dogs that did not develop postoperative infections. opinion, the literature does not provide convincing evi-
Several different limb‐sparing options are available, but a dence that any protocol is superior to single‐agent ther-
detailed explanation of the many techniques is beyond apy with carboplatin. Combined with the fact that
the scope of this chapter. carboplatin is generally well tolerated and is not associ-
Radiation therapy can also be used to treat local dis- ated with cardiotoxicity, the authors routinely recom-
ease in canine OSA cases. Full course curative intent mend single‐agent carboplatin. Additional prospective
radiation therapy is not routinely pursued due to the studies are needed to determine whether either of these
cost, side‐effects to adjacent tissue, and lack of benefit protocols is superior and to determine the optimal num-
when compared with standard surgical treatment. ber of doses. Cisplatin has shown significant efficacy and
Developing techniques such as stereotactic radiosurgery is considered standard of care for human osteosarcoma,
(SRS) and stereotactic body radiation therapy (SBRT), in but technical aspects and toxicity associated with admin-
which 1 to 5, high dose radiation treatments are deliv- istration coupled with the potential for renal toxicity
ered to the precise tumor location are showing promise. have made this protocol less often utilized in veterinary
SRS/SBRT have been shown to have comparable success patients. The administration of chemotherapy in the face
in some cases when compared to traditional surgical of gross metastasis is generally unrewarding, with
treatment; however, they continue to have limited avail- median survival times most often ranging from 30 to 90
ability due to the need for specialized equipment and days. Preliminary data support further studies to exam-
highly trained personnel. ine the potential of toceranib phosphate (Palladia™) to
Palliative radiation therapy may also be pursued for slow disease progression but no definitive conclusions
pain relief in cases where surgery is not possible or own- can be made to date.
ers do not elect for aggressive therapy. Generally, pallia- Multiple immunotherapy agents have shown some
tive radiation therapy involves the delivery of several efficacy either alone or in combination with chemother-
large doses of radiation in 2–4 fractions. Decrease in apy. These include liposomal muramyl tripeptide phos-
inflammation, slowing of osteolysis, and reduction in phatidyl ethanolamine (LMTPPE) and various delivery
tumor size are all benefits associated with palliative radi- methods of interleukin (IL)‐2. However, these agents
ation therapy. Over 50% of patients respond to therapy, are not commercially available and therefore are not
with onset of pain relief in 1–2 weeks and improvement routinely used.
lasting approximately 2–3 months on average. Aminobisphosphonates (ABPs) are a group of syn-
While it is reported that only approximately 10% of thetic analogs of organic pyrophosphate which possesses
dogs will have documented metastasis at the time of multiple potential benefits for patients with bone tumors
diagnosis, it should be noted that this number originates or bony metastasis. Generally, this class of drugs is con-
from dogs presenting to referral hospitals. It is therefore sidered palliative in that they can induce apoptosis of
possible that the incidence in primary care veterinary osteoclasts (inhibiting bone osteolysis), reduce pain,
clinics could be higher since thoracic radiographs are improve quality of life, and may delay progression of
often performed at the time of diagnosis, and referrals bony metastasis. In addition, in vitro studies have found
are probably less likely in dogs that have detectable that this class also exhibits direct cytotoxic effects on
metastases. Even though 90% of dogs will have no osteosarcoma cell lines. While oral ABP formulations are
detectable pulmonary metastasis, with rare exceptions, available, this route of administration does not reach