Editors' Note: This case was presented in a session entitled "Case studies in cancer pain management" during the International Veterinary
Academy of Pain Management (IVAPM) symposium at CVC Kansas City, Aug. 30, 2009.
Tatou, a 9-year-old 92.4-lb (42-kg) neutered male Labrador retriever, was presented to the Hopital Veterinaire Rive-Sud oncology
service for evaluation of a subcutaneous mass on the lateral aspect of the left antebrachium (Figure 1). The mass was associated with intermittent weight-bearing lameness that responded poorly to carprofen and tramadol; the
latter caused anorexia, according to the owners.
Plain radiographs of the left forelimb demonstrated an aggressive mixed bone lesion in the ulnar diaphysis with osteolysis
and some bone proliferation (Figure 2). Three-view thoracic radiographs obtained on the same visit did not show detectable pulmonary metastasis. Results of a complete
blood count and serum chemistry profile and urinalysis were all normal except for an elevated alanine transaminase (ALT) activity
(522 U/L; reference range = 10 to 100 U/L).
Fine-needle aspirates of the subcutaneous mass were obtained with a 22-ga needle and submitted for cytologic evaluation and
staining for alkaline phosphatase (ALP) activity. A population of mesenchymal cells with small amounts of eosinophilic matrix
consistent with osteoid was observed (Figure 3), and positive staining for ALP activity was demonstrated (Figure 4), suggesting a diagnosis of osteosarcoma.
Because the tumor clearly extended in the extraosseous subcutaneous tissues of the antebrachium, an ulnectomy could not be
recommended since complete surgical margins could not be obtained. Thus, the therapeutic options discussed included standard
therapy combining amputation of the left forelimb and adjuvant chemotherapy as well as palliative options such as hypofractionated
radiation therapy, intravenous aminobisphosphonate administration (pamidronate or zoledronate), and oral analgesic therapy.
The owners declined amputation and any injectable therapy. Because of the elevated ALT activity, they were instructed to discontinue
carprofen administration, but they initially refused adjuvant analgesic therapy. Three weeks later, with the ALT activity
back in the normal range, deracoxib was prescribed (1.2 mg/kg orally once a day). A good clinical response was observed with
complete resolution of the lameness.
Upon recheck visits over the next 12 months, Tatou was found to have an excellent quality of life and appeared perfectly comfortable
with no evidence of detectable lameness or discomfort. The subcutaneous mass was noted to grow slowly over time. The results
of periodic serum chemistry profiles were normal.
Thirteen months after diagnosis, the weight-bearing lameness recurred. A radiographic examination of the left forelimb showed
progression of the bone lesion with more destruction and a larger soft tissue component. Thoracic radiographs then revealed
advanced pulmonary metastatic lesions measuring up to 50 mm in diameter (Figure 5). The owners understood that the prognosis was guarded for survival but were instructed that additional analgesic therapy
could be used to make Tatou more comfortable.
We opted to continue therapy with deracoxib because it was well-tolerated and provided adequate analgesia in monotherapy for
more than a year and because the recurring pain and lameness were thought to be due to an increased level of pain rather than
decreased analgesic efficacy of the drug itself. Tramadol hydrochloride was prescribed at a dosage of 4 mg/kg orally twice
a day, as well as amantadine at a dosage of 5 mg/kg orally once a day.
Other palliative therapies were again discussed, such as radiation therapy or aminobisphosphonates (oral or injectable), but
were declined. Nevertheless, Tatou responded well to the changes in medication, and the lameness again rapidly and completely
Tatou had an excellent quality of life for two additional months, but presented one day following an acute episode of nonweight-bearing
lameness. A radiograph of the left forelimb confirmed a pathologic fracture of the ulna and the radius (Figure 6). The owners then opted for euthanasia, 445 days after diagnosis.
This case demonstrates that, though unusual, certain cases of cancer may respond well to conservative analgesic therapy initially
but eventually require multimodal analgesia for proper control once pain progresses and becomes more severe. It also demonstrates
that despite a poor prognosis once advanced metastasis is detected, palliative therapy to improve comfort should be considered
and may result in added months of excellent quality of life.
Louis-Philippe de Lorimier, DVM, DACVIM (oncology)
Hôpital Vétérinaire Rive-Sud
7415 Boulevard Taschereau
Brossard (Québec) J4Y 1A2, Canada