Introduction

Osteosarcoma is a devastating disease in dogs, with 8000–10,000 new canine osteosarcoma diagnoses annually.¹ Treatment consists of local control and systemic therapy. Local therapy aims to control the local disease and to treat the pain caused by the tumor or the pathologic fractures secondary to the tumor. Surgical treatment for local control can entail a limb-sparing technique^2–20 or an amputation.^{2,7,9,17,21–26} Another option for local tumor control is stereotactic radiosurgery²⁷ or radiotherapy²⁸ in conjunction with stabilization if needed.

Systemic therapy is aimed at treating the metastatic disease by systemic chemotherapy,^{3,7,9,23,25,26,29–39} although surgical metastasectomy²⁶ can be performed in select cases. Median survival with amputation alone has been reported to be 19.2 wk (162 dogs).⁴⁰ Reported median survival times were 262–413 days after surgery and cisplatin chemotherapy,^2,17,41,42 307 days after surgery and carboplatin chemotherapy,²⁴ and 235–540 days^7,29,43,44 after surgery and a combination of doxorubicin and carboplatin. Besides clinical stage, several factors have been associated with shorter disease-free interval and survival time, such as location (proximal humerus),^45,46 age,⁴⁶ weight,⁴⁶ elevated monocyte count,⁴⁷ and serum alkaline phosphatase (ALP).^45,46,48

As our ability to treat metastasis improves, effective local control of recurrence will become a greater issue. A chemotherapeutic agent instilled into the wound bed at the time of surgery could improve local disease control in cases in which limb-sparing surgery is pursued. Reported local recurrence rates (within the current survival times) after limb-sparing surgery range from 15 to 28%.^{10,19,34,49,50} Locally delivered platinum chemotherapeutic agents, such as carboplatin and cisplatin, have been used as adjunctive therapy for osteosarcomas^19,38,51 and soft-tissue sarcomas⁵² either as a single agent or as part of a multidrug protocol.

Poloxamer 407 is a nonionic polyoxyethylene-polyoxypropylene-polyoxyethylene. It changes from a liquid to a gel when warmed to temperatures higher than 25°C.^5,6 This property has been shown to make this specific poloxamer copolymer gel a good carrier medium for prolonged local antifungal therapy⁵ and might show the same promise for prolonged local chemotherapeutic administration. Prior studies have shown that carboplatin is stable in poloxamer carriers.^13,14 These carriers fully release carboplatin in vitro⁵³ and do not cause any macroscopic necrosis or wound healing complications when implanted subcutaneously (5 mg/mL) in rats.⁵⁴ This report describes the outcome after use of carboplatin in poloxamer 407 in a clinical patient with a marginally excised ulnar osteosarcoma.

Case Report

An 8 yr old male castrated hound mix (45.5 kg body weight) was presented to the North Carolina State University Small Animal Surgery Service for further evaluation of a suspected osteosarcoma of his left distal ulna. He initially presented to his local veterinarian after a 4 wk history of left thoracic limb lameness. Osteosarcoma was tentatively diagnosed based on radiographic findings of an aggressive bony lesion (Figure 1) and confirmed by histopathology based on a biopsy. At presentation, a 2 out of 4 localized pain was present on palpation of the distal aspect of the left ulna after splint removal. The dog showed decreased range of motion in both elbows, as well as mild to moderate pain on hip extension bilaterally. All other physical examination findings were within normal limits.

View Figure

• Download as Powerpoint
• Download Figure

Bloodwork performed prior to his referral showed a monocytosis (0.945 × 10³/UL, range 0.075–0.85 × 10³/UL), slight hyperglycemia (141 mg/dL, range 70–131 mg/dL), hyperphosphatemia (6.7 mg/dL, range 2.5–5.6 mg/dL), marked elevation in ALP (346 IU/L, range 16–140 IU/L), and slight elevation in alanine transaminase (67 IU/L, range 12–54 IU/L). The remainder was unremarkable. The dog was normoglycemic on follow-up bloodwork the next 2 days during his stay at the North Carolina State University Small Animal Surgery Service. ALP remained markedly elevated on subsequent bloodwork: 655 IU/L (347 days), 377 IU/L (370 days), and 805 IU/L (444 days after initial diagnosis).

On preoperative computed tomography^a (CT; 31 days after initial tentative diagnosis), an aggressive bony lesion of the distal aspect of the left ulna was confirmed and further delineated (Figure 1). The distal ulnar cortex showed concentric lysis in conjunction with radiating periosteal reaction. A pathologic ulnar fracture was evident in the distal aspect of the mass. The radial bone adjacent to the mass radiographically appeared normal with no evidence of periosteal reaction. CT imaging of the chest revealed no evidence of pulmonary metastatic disease. No bone metastases were noted on scintigraphy (21 mCi of Technetium^b MDP IV). Indication of degenerative joint disease was present as evidenced by mild uptake in multiple joints, including the right elbow joint, the right stifle joint, and the left coxofemoral joint.

Surgery was performed 2 days after the CT scan (33 days after initial tentative diagnosis). A combination of hydromorphone 0.1 mg/kg intramuscularly and dexmedetomidine^c 5 μg/kg intramuscularly were given as premedication. The patient was intubated endotracheally after induction with propofol^d 4 mg/kg IV to effect and maintained with isoflurane^e in O₂. A radial, ulnar, median, and musculocutaneous nerve block with bupivacaine^f 1 mg/kg was performed proximal to the surgery site in the affected leg for additional local analgesia. Surgical analgesia was maintained with fentanyl^g 0.3 μg/kg/min IV. Antibiotic prophylaxis was given every 120 min during the surgical procedure (cefazolin^h 22 mg/kg IV). Monitoring of SpO₂, end-tidal CO₂, direct blood pressure, and anesthetic depth was performed and recorded at regular intervals during anesthesia. The patient was placed in right lateral recumbency for the surgery, with the left antebrachium clipped and aseptically prepared to include the toes, axilla, and scapula. A 10 cm incision was made on the caudolateral side of the distal left antebrachium, including a 4 cm elliptical portion of skin overlying the ulnar mass that included the previous biopsy site. The tissues were dissected bluntly until the periosteum could be identified at the proximal ulna. The soft tissue around the tumor was carefully dissected away to avoid seeding the tumor and a small section of extensor muscle was excised. A 10 cm portion of the ulna was removed using a bone saw, beginning mid-shaft and extending to within 5 mm of the distal edge of the styloid process. Touch impressions were obtained of the distal and radial surface of the excised ulna. Carboplatinⁱ in poloxamer 407^j was compounded by mixing an equal volume of 10 mg/mL carboplatinⁱ with poloxamer 407^j under sterile conditions approximately 15 min before use. A total dose of 27 mg of carboplatin (tumor volume of 18 cm³) was instilled in the void, with the volume (5.4 mL) being the dose-limiting factor. The muscles and connective tissues at the proximal and distal ends of the wound were approximated over the carboplatinⁱ in poloxamer 407^j and the remainder of the incision was closed routinely.

Postoperative radiographs (Figure 1) were taken, after which a soft padded bandage with an incorporated fiberglass^k splint was applied for support. No bone lysis was detected in any of the surrounding bones on the postoperative radiographs. Analgesia was ensured postoperatively with a combination of IV pain medication: fentanyl^g 3 μg/kg/hr, ketamine^l 0.1 mg/kg/hr, lidocaine^m 2% at a rate of 30 μg/kg/min, and carprofenⁿ. The patient was gradually taken off IV analgesia and was discharged 2 days after surgery on oral carprofenⁿ to complement a 100 μg/hr fentanyl patch^o placed the evening prior to discharge. The bandage was changed daily for the first postoperative week and every 2–3 days for the 2 wk thereafter to inspect the wound for any healing complications. The incision site healed uneventfully. No local or systemic side effects of the locally administered carboplatin were noted.

Histopathology revealed an osteosarcoma, with 7 mitotic figures observed in 10 high-magnification fields (2.37 mm²). Toward the proximal aspect of the ulna, a 3.5 cm tumor-free margin was obtained, whereas distally, a 1 cm tumor-free margin was obtained. No tumor cells were detected in any margin.

The patient received four doses of carboplatinⁱ IV (250 mg/m² at 30 and 51 days, and 300mg/m² at 79 and 100 days after surgery, respectively), with the first dose intentionally decreased as a precaution owing to the intralesional therapy. No delay in treatment was needed as a result of the intraoperative dose of carboplatinⁱ, as neither incisional nor myelosuppressive effects were documented after surgery. The WBC and neutrophil count 15 days postoperatively were 11.5 (10³/µL), and 8395/µL, respectively. No evidence of pulmonary metastases was present at any of the serial recheck thoracic radiographs performed every 3 mo up to time of euthanasia. ALP remained elevated on subsequent bloodwork: 346 U/L on presentation (reference range 16–140 U/L), 655 U/L (reference range 16–140 U/L; 347 days), 377 U/L (reference range 16-140 U/L; 370 days), and 805 U/L (range 20–150 U/L; 444 days after initial diagnosis).

On radiographs performed 330 days after initial diagnosis (296 days after surgery), a moderate, ill-defined mineral opacity was visible in the distal aspect of the surgical site, surrounded by a moderate soft-tissue swelling (Figure 2). Adjacent to this soft-tissue mineralization, an ill-defined lytic area of the caudal cortex of the distal metaphysis and epiphysis of the radius was visible. The distal aspect of the proximal ulnar remnant was unremarkable. A fine-needle aspiration confirmed recurrence of osteosarcoma. A CT study centered on the left forelimb was performed (18 days later; 347 days after initial diagnosis, 313 days after surgery). The CT showed a non–contrast-enhancing mineral density lesion in the subcutaneous tissues caudal to the left radius starting approximately 3.1 cm proximally from the radiocarpal joint and ending just proximal to the level of the left accessory carpal bone. In the adjacent distal radius, a moth-eaten lysis with near complete destruction of the cortical bone was present, as was a focal area of lysis along the dorsomedial distal cortex, with evidence of a pathologic fracture. A moderate amount of irregularly margined periosteal reaction was associated with the lysis. The associated soft tissues appeared moderately swollen and mildly contrast enhancing. These findings were most consistent with local recurrence of the previous osteosarcoma at the surgical site. There was no evidence of involvement of the remaining ulna. Although no evidence of local lymph node metastasis was appreciated on CT imaging, there was evidence of a contrast-enhancing soft-tissue mass craniodistal to the left humerus. A scintigraphy scan (313 days after the first surgery; similar protocol) revealed a severely increased radiopharmaceutical uptake at the distal aspect of the left antebrachium corresponding to the distal aspect of the previous ulnectomy site, indicating local recurrence. No contrast uptake was detected at the proximal aspect of the surgery site. Within the soft tissues craniodistal to the left shoulder, a rounded area of severely increased radiopharmaceutical uptake was visible, consistent with the previously reported subcutaneous mass craniodistal to the humerus on CT. A focal area of increased radiopharmaceutical uptake was visible on the left 13th rib. Given the history of the patient, both findings were most consistent with metastatic lesions. Increased uptake was again noted in several joints including the right elbow, left coxofemoral, and right tarsocrural joints, but this time not in the right stifle joint, presumably owing to a small difference in patient positioning. Three-view thoracic radiographs were taken the following day to further investigate the region of uptake in the left 13th rib, which showed an irregular periosteal reaction and focal destruction of the rib, consistent with an aggressive lesion. This lesion is in the same area as the previously noted increased radiopharmaceutical uptake seen in the nuclear medicine study.

View Figure

• Download as Powerpoint
• Download Figure

A full limb amputation was recommended and performed (342 days after initial surgery, 376 days after initial diagnosis) because of the pain associated with the recurrence and pathologic fracture. A minor wound revision was performed 22 days after amputation for a superficial surgical site infection, and the incision healed without complications.

The patient was euthanized 445 days after the initial diagnosis (411 days after the first surgery) as a result of nonambulatory paraparesis combined with hyperesthesia on palpation of the thoracolumbar spine. CT imaging showed presumed metastases in caudal thoracic, 2nd lumbar, and sacral vertebrae.

Discussion

The patient in this report received 27 mg total carboplatin intralesionally using poloxamer 407 as a carrier after ulnectomy for an ulnar osteosarcoma. No short- or long-term wound healing complications were noted after local delivery of carboplatin poloxamer 407. Survival time was 445 days from the initial diagnosis, and local recurrence was 296 days after surgery. As a precaution, the initial dose of chemotherapy was decreased to 250 mg/m². Neither systemic side effects nor myelosuppression was observed on subsequent bloodwork, and the postoperative chemotherapy was performed as scheduled. Prior rodent pharmacokinetic studies investigating poloxamer 407 as a carrier have shown a sustained local tissue concentration of carboplatin at 7 days, with a systemic half-life of 34 hr.⁵⁴ Given these findings, it does not appear that systemic chemotherapy needs to be delayed beyond suture removal after local administration of carboplatin in poloxamer at the time of surgery.

Local delivery of chemotherapeutic agents involving platinum drugs has been reported using several delivery systems in clinical patients following incomplete tumor resection.^19,51,52,55 Open-cell poly lactic acid with cisplatin (OPLA-Pt) was investigated as a local therapy in limb-sparing surgery in a randomized, prospective trial.¹⁹ This compound was placed in the surgery site of appendicular osteosarcoma removed from the bone without amputation (limb-spare).¹⁹ Limb-spare patients treated with OPLA-Pt were found to have a 55% lower chance of local recurrence; however, there was an overall surgical site infection rate of 47%.¹⁹ In a second study investigating the same local delivery system, a 36% local complication rate was seen.⁵¹

A different, in situ forming injectable implant containing cisplatin (Atrigel) was used in combination with marginal surgery for extremity soft-tissue sarcomas.⁵² With this compound, the local recurrence rate was 16.6%, similar to the 17% recurrence rate after marginal resection and radiation therapy.⁵⁶ Unfortunately, local complications were seen in 84% of cases and could be further divided into minor (11/19 cases) and severe (5/19 cases).⁵²

In vitro release of carboplatin from poloxamer 407 was shown to be faster than release from calcium hemi-hydrate beads and complete by 24 hr.⁵³ Local subcutaneous implantation of carboplatin in poloxamer 407 in rats showed no wound or systemic complications,⁵⁴ and sustained local concentrations remained at 7 days. Plasma concentration peaked at 24 hr with a half-life of 34 hr.⁵⁴

In a multi-institutional retrospective paper on ulnar osteosarcoma, median survival time was 463 days. Fifteen (out of 30 included) patients developed distant metastases, of which 6 were bone metastases.⁵⁰ Prior reported recurrence rates after limb-sparing surgery for osteosarcoma range from 15 to 28%,^{10,19,34,49,50} with 1 out of 11 ulnectomy cases recurring at 210 days.⁵⁰ The use of local chemotherapeutic agents during limb-sparing surgery has been reported previously. A larger study on local use of OPLA-Pt during limb-sparing surgery for osteosarcomas showed that local recurrence occurred at a mean of 325 days (no local treatment) and a mean of 347 days (OPLA-Pt). Local recurrence was 832 days after complete resection versus 256 days after a marginal excision.¹⁹ An additional study reported recurrence in one dog at 210 days with a median follow-up of 307 days (108–1077 days).⁵⁰ Resection in the current case was wide proximally and distally. Because of the location of the tumor and the planned preservation of the radius, there was concern for the margins toward the radius and surrounding tissues. This prompted the decision to add adjunctive local therapy (carboplatin in poloxamer 407) into the wound bed. Although no tumor cells were visualized at any of the cut margins, wide margins could not be obtained at the level of the radius as anticipated. The recurrence time (296 days after surgery) compares well to other reported cases with marginal resection and local chemotherapy¹⁹ but is difficult to compare to the existing ulnectomy-only literature (1 out of 11 recurred at 210 days; follow-up time of 108–1077 days).⁵⁰

No local or distant adverse effects were noted from the local delivery system of carboplatin in poloxamer 407. The case in the current report did develop local recurrence (at 296 days after surgery) and distant metastases. Although further efficacy studies are needed, carboplatin in poloxamer 407 appears to be an easy and safe method for local adjunctive therapy after a marginal or incomplete tumor resection.