Osteosarcoma in the dog and cat

Osteosarcoma is a malignancy that occurs in both the dog and cat. In the dog it accounts for 85-98% of bone tumours (Liptak et al., 2004b; Dernell et al., 2007).The tumour develops more frequently in the appendicular skeleton (75%) but can also occur in the axial skeleton (24%) and rarely in extra-osseous sites (1%) (gastrointestinal tract, liver, subcutaneous tissue, bladder, kidney, thyroid, eye).

In the cat osteosarcoma is the most common bone tumour, constituting 70-80% of tumours of the bone. It usually develops in animals aged between 8-10 years old, without a particular gender or breed predisposition, although there are descriptions of cases in younger animals. In the cat, the lesions are equally frequent in appendicular bones (particularly, unlike in the dog, in the hind limbs) and in the axial skeleton (skull, pelvis, ribs, vertebrae), and more frequent in extra-osseous sites (35-40%), including the mammary gland, eye, liver and bowel, but above all at the site of vaccination (injection-induced sarcoma). Whereas metastases are very common in the dog (80-90% of cases) the frequency of metastatic spread in the cat is low (5-10%), although this is a locally very aggressive tumour able to lyse the surrounding bone (Fig. 1). The treatment of choice, given the tumour’s biological tendency to lesser metastasis, is surgical resection with wide margins. The prognosis of appendicular tumours is, therefore, better than that of the axial or extra-osseous forms of osteosarcoma, since in these latter cases it is not always possible to excise the tumour with wide, tumour-free margins. The survival of cats with appendicular osteosarcoma managed with amputation of the affected limb, without chemotherapy, ranges from 24 to 44 months; this is longer than the survival of animals with axial osteosarcoma (mean survival, 6 months). For these latter cases, results can be improved by using multimodal treatment based on a combination of surgery, radiotherapy and/or chemotherapy. The rate of local recurrence after only surgery can be high (44%) and depends on how radical the resection is. The onset of osteosarcoma following exposure to radiation or in animals with long-term bone fixation systems has been reported also in cats. The clinical signs vary depending on the site of the tumour but include mainly lameness and body deformities (Fig. 2). The diagnostic strategy is the same as that for the dog, described below. The prognosis is influenced not only by the site of the tumour, but also by its histological grade and mitotic index (Heldmann et al., 2000; Dernell et al., 2007; Dimopoulou et al., 2008).

OSTEOSARCOMA OF APPENDICULAR BONE

BIOLOGICAL BEHAVIOUR

Osteosarcoma of appendicular bone is locally very aggressive, causing lysis of bone and secondary invasion of surrounding tissues; it is also highly metastatic, with haematogenous spread to the lungs and secondarily to the bone, viscera, skin, subcutaneous tissue and brain (Gorman et al., 2006; Dernell et al., 2007). Metastases can also be found in the tributary lymph nodes (4-9%) (Brodey et al., 1976; Spodnick et al., 1992; Hillers et al., 2005).

LOCALISATION

Osteosarcoma more often occurs in the metaphyseal region of long bones and does not cross the adjacent joint. The anterior limbs are involved twice more frequently than the posterior limbs; the distal radius and proximal humerus are the most frequently affected sites, followed by the distal and proximal femur and the distal tibia (Straw et al., 1990; Dernell et al., 2007). Heavy dogs and giant breeds are affected; in fact, only 5% of cases of osteosarcoma develop in animals weighing less than 15 kg (Dernell et al., 2007). The Greyhound, Rottweiler, Great Dane, St. Bernard, Dobermann Pinscher, Irish Setter, Golden Retriever and German Shepherd dog seem to be more at risk, but more because of their size than because of factors related to breed (Ru et al., 1998; Rosenberg et al., 2007). A family predisposition has been described in the St. Bernard, Rottweiler and Scottish Deerhound (Misdorp, 1980; Phillips et al., 2007).

SIGNALMENT

Male animals have been reported to be affected slightly more frequently than females, although this has not been confirmed by some authors (Brodey et al., 1976; Mauldin et al., 1988; Shapiro et al., 1988; Kraegel et al., 1991; Spodnick et al., 1992); the females affected are particularly of the St. Bernard, Great Dane and Rottweiler breeds. Osteosarcoma usually develops in dogs 7-9 years old, but can be found in younger animals (18-24 months) (bimodal distribution) (Dernell et al., 2007).

AETIOLOGY AND RISK FACTORS

The aetiology of osteosarcoma is still unclear, but some factors that can contribute to the onset of the tumour have been identified. These include:

• Ionising radiation

The role of ionising radiation has been demonstrated both clinically and experimentally. There are case reports of the development of osteosarcoma (vertebral, oral, appendicular) as a late complication (from 1.7 to 5 years after treatment) following radiotherapy (cobalt teletherapy, megavoltage and orthovoltage radiotherapy) (Dickinson et al., 2001; Gillette et al., 1990; Thrall, 1984; White et al., 1986; Powers et al., 1989). Experimentally, tumour growth has been induced in some Beagles treated with a plutonium dioxide-based aerosol or intravenous doses of _²³⁹plutonium citrate or _²⁴¹americium (Muggenburg et al., 1996; Lloyd et al., 1993 and 1994).

• Chronic trauma

Metal implants left in position for a long time (for example, intramedullary nails, old generation plates for tibial plateau levelling osteotomy) can induce the development of osteosarcoma (Sinibaldi et al., 1976; Sinibaldi et al., 1982; Murphy et al., 1997; Boudrieau et al., 2005; Harasen et al., 2008) (Fig. 3).

This occurs as the result of corrosive phenomena related to the composition of the metal implant, secondary infections or instability of the fixation system (Stevenson, 1991). Nevertheless, it should be emphasised that given the very large number of fixation systems used in the history of veterinary orthopaedic surgery and the lack of concrete scientific proof of a connection, the development of sarcomas could simply be a coincidence (Murphy et al., 1997).

Furthermore, cases of osteosarcoma have been described following spontaneous bone infarcts or secondary to orthopaedic surgery and following osteochondritis dissecans (Riser et al., 1972; Dubielzig et al., 1981; Marcellin-Little et al., 1999; Holmberg et al., 2004). There is also the report of a case of osteosarcoma that developed in the stifle joint of dog in which a gauze had been accidently left in the joint following repair of an anterior cruciate ligament (Miller et al., 2006).

For a long time it was believed that microtrauma of the metaphysis of the distal radius of large dogs was one of the most important risk factors for the development of osteosarcoma. This hypothesis was disproved by the results of a study carried out by Gellash (2002) on two groups of dogs of different size (<15 kg; >25 kg).

• Genetic modifications

Mutations have been described in the tumour suppressor gene p53 and in PTEN (Levine et al., 2002). Abnormalities that have been observed in dogs with osteosarcoma and identified as negative prognostic factors include (Kirpensteijn, et al., 2008; Sagartz et al., 1996; Loukopoulos et al., 2003; van Leeuwen et al., 1997; Mendoza et al., 1998) over-expression of erb-B2; (Flint et al., 2004) expression of hepatocyte growth factor (HGF) and its receptor, c-Met has been found in many cases of canine osteosarcoma; (Ferracini et al., 2000; De Maria et al., 2009; Fieten et al., 2009); it has been demonstrated in vitro that insulin-like growth factor-1 (IGF-1) and its receptor IGF-1R play a role in the growth and invasion of osteosarcoma (MacEwen et al., 2004); in vitro and in vivo expression of matrix metalloproteinases 2 and 9 which have a role in the local and metastatic spread of the tumour (Lana et al., 2000; Loukopoulos et al., 2004); the expression of ezrin, a cytoskeletal protein in osteosarcoma in puppies has been associated with the early development of metastases and a worse prognosis (Khanna et al., 2004).

SIGNS AND SYMPTOMS

The appendicular forms of osteosarcoma are characterized by swelling of the affected limb, which may be more or less evident depending on the bone district involved, pain and tenderness to palpation (Fig. 4). Often there is pain secondary to activation of the periosteum, intermittent and mild lameness in the early stages which tends to become persistent and severe over time (video) and a variable degree of muscle wasting which may or may not appear early in the course of the disease. Lameness of acute onset together with a total lack of weight-bearing are often indicators of pathological fractures. These are more frequent in cases of haemangiosarcoma, multiple myeloma and metastatic and infiltrative tumours (Dernell et al., 2007).

DIAGNOSIS AND STAGING

The signalment and clinical signs are alone often indicative of bone tumours. The diagnostic work-up must, in all cases, include:

• a thorough physical examination
• X-rays
  • of the primary lesion with cranio-caudal and latero-medial views which must also include the joint proximal or distal to the bone defect and the contralateral limb. The radiographic appearance of appendicular osteosarcoma is characterized by variable signs of lysis of the bone cortex, new bone growth, periosteal proliferation, new subperiosteal bone growth, swelling of adjacent soft tissues and, sometimes, calcification (Fig. 5).
  • of the thorax in right and left latero-lateral, ventro-dorsal or dorso-ventral views in order to stage the tumour by evaluating any metastatic spread into the lungs (Fig. 6). Pulmonary metastases are present at the time of diagnosis in less than 5-10% of patients. It should, however, be remembered that appendicular osteosarcoma is highly metastatic and about 90% of the dogs have micrometastases that are not radiographically visible; these subjects will develop macroscopic metastases within 1 year of treatment if managed with only amputation of the affected limb (Dernell et al., 2007). Computed tomography (CT) is more sensitive than radiography in detecting small pulmonary lesions (Nemanic et al., 2006).

• cytological examination of material collected by needle aspiration. This is a simple, non-invasive method that can be performed in the presence of lytic bone lesions to confirm the clinical and radiographic suspicion of a bone tumour (Loukopoulos et al., 2005; Reinhardt et al., 2005; Britt et al., 2007). It is diagnostic in about 50% of cases.
• histological examinationof a bone biopsy obtained using a Jamshidi needle (Fig. 7), incision or Michelle trephine. The Jamshidi needle can usually obtain a good sample without the risk, present with the Michelle trephine, of causing pathological fractures. This is the investigation of choice for reaching a definitive diagnosis (and should always be performed in the case of a suspected bone tumour). The diagnostic quality of the sample (whether cytological or histological) can be improved by taking the biopsy under guidance (ultrasound, computed tomography, image intensification) (Vignoli et al., 2004; Britt et al., 2007). It is important to take the sample from deep within the core of the lesion, in order to avoid sampling superficial parts of the lesion which are often only reactive bone.
• blood tests,including alkaline phosphatase in the case of osteosarcoma.

It should be remembered that a small percentage of osteosarcomas can metastasise to lymph nodes (<10%) and other bone districts (7.9%). Tumour staging should, therefore, include clinical palpation or diagnostic imaging (computed tomography, ultrasonography) of the draining lymph nodes, and needle biopsy of these nodes. Likewise, bone scintigraphy, if available, should be performed to reveal lesions not yet radiographically evident in bone. Any lesions detected must be biopsied because scintigraphy is not specific for metastases (i.e. detected lesions may be due to infections or arthritis, besides malignancies).

The clinical staging of osteosarcoma is detailed in the table below.

Table 1. TNM staging of primary bone tumours (modified from Owen LN.TNM classification of Tumours in Domestic Animals, WHO, Geneva, 1980).

TREATMENT

Dogs with appendicular osteosarcoma can be given palliative treatment, with the purpose of relieving pain, or be managed with a curative intent aimed at controlling the local disease and preventing or delaying metastatic disease.

Limb amputation
Limb amputation is non-conservative surgery and is the most effective way of achieving local eradication of the tumour (Brodey et al., 1976; Spodnick et al., 1992). It is performed by separation of the coxo-femoral joint when a posterior limb must be amputated and by detachment of the scapula from the trunk in the case of anterior limb amputation. It eliminates the risk of pathological fractures, relieves pain and, for most sites of appendicular tumours, enables a wide surgical margin free of tumour to be obtained. It is an operation virtually free of complications and is functionally acceptable, even in heavier dogs which manage to walk anyway and to carry out their main functions (video). Most owners are satisfied with the quality of life of their animals (Carberry et al., 1986; Kirpensteijn et al., 1999). Contraindications to amputation include severe obesity and concomitant, debilitating orthopaedic or neurological disorders.

Limb salvage
Osteosarcoma can be controlled locally, sparing the limb from amputation, by surgery or radiotherapy. Excellent results have been obtained with conservative surgery for osteosarcomas located in the distal radius, ulna, metacarpus, metatarsus and ischium, while functional results for osteosarcomas in other sites have not been satisfactory and the rate of complications is high (Kuntz et al., 1998; Morello et al., 2001).

Limb-sparing techniques, involving conservative surgery, have been under study in veterinary practice, for some sites (distal radius), for many years. The tumour is resected with wide margins (3-4 cm), on the basis of measurements made on the pre-operative computed tomography or magnetic resonance imaging scans (Leibman et al., 2001; Wallack et al., 2002; Davis et al., 2002). Following asportation of the tumour, the site must be reconstructed with:

• frozen bone from a biobank (homologous bone graft) (LaRue et al., 1989; Morello et al., 2001; Liptak et al., 2004a);
• a metal prosthesis (Liptak et al., 2006) (Figs. 8 and 8a);
• excised neoplastic bone after neutralisation of the tumour cells by pasteurisation (65° C for 40 minutes in sterile physiological saline) (autologous bone graft) (Buracco et al., 2002; Morello et al., 2003) (Fig. 9);
• an excised, autoclaved segment of neoplastic bone (Massin et al., 1995; Yamamoto et al., 2002);
• an excised, irradiated segment of neoplastic bone (Yamamoto et al., 2002; Liptak et al., 2004c; Boston et al., 2007)

Bone or metal implants are fixed to the host’s proximal and distal bone stumps by dynamic compression plates, with arthrodesis of the joint adjacent to the tumour. Conservative surgery for an osteosarcoma of the proximal femur, combining homologous bone grafting with a prosthetic implant, has also been performed (Liptak et al., 2005).

Conservative surgery with the above-mentioned techniques is not, however, free of complications, such as infections (31-60%), breakage or collapse of the fixation system (11-40%) and local recurrence of the neoplasm (15-28%) (LaRue et al., 1989; Straw et al., 1996; Morello et al., 2001; Morello et al., 2003; Liptak et al., 2006). Infections of the graft – fixation system can be of variable severity. The most frequent forms are recurrent cutaneous fistulae, which can be treated by periodic administration of antibiotics and local disinfection of the lesions. In the more severe cases, osteomyelitis may develop; amputation of the limb is the only solution in this case.

Besides the above listed techniques, another strategy that can be used following excision of an osteosarcoma from the radius or distal tibia is to fill the defect with viable, vascularised, regenerated bone through progressive distraction achieved by applying a modified Ilizarov’s apparatus for single (Figs. 10 and 10a) or double longitudinal or transverse bone transport (Tommasini-Degna et al., 2000; Rovesti et al., 2002; Ehrhart, 2005; Jehn et al., 2007).

Salvage of a limb affected by osteosarcoma of the distal radius has also been achieved by rotating the ulna, with its vascular pedicle, into the defect left by excision of the tumour (vascularised autologous graft) (Seguin et al., 2003). Biomechanical complications following this technique  have been described (Pooya et al., 2004).

If used alone, surgery should be considered as mere palliation. The mean survival of dogs treated with only surgery varied from 103 to 175 days (Brodey et al., 1976; Mauldin et al., 1988; Shapiro et al., 1988; Straw et al., 1991; Thompson and Fugent, 1991; Berg et al., 1992; Spodnick et al., 1992) and the survival rates at 1 and 2 years were, respectively, 11-20% and 2-4% (Straw et al., 1991; Thompson and Fugent, 1991; Berg et al., 1992; Spodnick et al., 1992). In contrast, the survival rates of amputated subjects and those treated with conservative surgery are similar when the conservative surgery is combined with chemotherapy (Straw et al., 1996). There are, however, differences among patients undergoing limb-sparing techniques (homologous grafts, autologous grafts, metal prostheses) depending on whether the animals develop infection; dogs that develop an infection of the graft survive longer than those which do not develop an infection (685 versus 289 days) (Lascelles et al., 2005; Liptak et al., 2006).

Chemotherapy
Chemotherapy combined with surgery or radiotherapy is able to prolong the survival of dogs with appendicular osteosarcoma, increasing from mean survival times of 103-175 days without chemotherapy to 262-450 days with chemotherapy (Brodey et al., 1976; Mauldin et al., 1988; Shapiro et al., 1988; Straw et al., 1991; Thompson et al., 1991; Berg et al., 1992; Spodnick et al., 1992). The 1- and 2-year survival rates in animals treated with chemotherapy are 31-48% and 10-26%, respectively  (Straw et al., 1991; Thompson et al., 1991; Berg et al., 1992; Spodnick et al., 1992). The chemotherapeutic agents most widely used in the treatment of osteosarcoma in animals include doxorubicin, cisplatin, carboplatin and lobaplatin, administered alone or in combination with each other (Table 2).

The survival of dogs treated exclusively with a platinum-derived drug (carboplatin, cisplatin) is similar to that obtained from using combined protocols (Dernell et al., 2007). It is not yet clear which of the drugs is the most effective nor what is the best time to start chemotherapy. Usually adjuvant therapy is started in the post-operative period, leaving time for the patient to recover from the surgery and for the wound to heal (Berg et al., 1997; Dernell et al., 2007). Indeed, since the really efficacy of early initiation in the post-operative period has not been proven, it is advisable to wait for 7-10 days.

Chemotherapy has also been applied locally, in the form of cisplatin-soaked, slow-release, biodegradable sponges, in the site of surgery in the case of bone grafts (Straw et al., 1994; Withrow et al., 2004; Mehl et al., 2005).

Chemotherapy is aimed at the malignant micrometastases and is, in fact, less effective when used to treat macroscopic metastases (Ogilvie et al., 1993). These latter can be managed, when appropriate, by excision (O’Brien et al., 1993).

Table 2. Chemotherapy protocols in use for canine osteosarcoma and relative survival data.

Radiotherapy
Radiotherapy has been used with curative intent combined with chemotherapy without surgery, but with less satisfactory oncological results than those achieved with the combination of surgery and chemotherapy (Walter et al., 2005). Radiotherapy has also been combined with chemotherapy in protocols in which the bone segment containing the neoplasm is externalised by surgery and then irradiated with a single dose of 70 Gy radiation. The complication rate of this procedure is, however, high (69%) with infections, fracture of the irradiated bone, recurrence and collapse of the fixation system all having been reported (Liptak et al., 2004c; Boston et al., 2007). Stereotactic radiosurgery has been used recently, with good to excellent results; this is a modern treatment modality designed to treat tumours in a single session with high power radiation (30-50 Gy), targeted carefully on the tumour in order to minimise irradiation to surrounding tissues. In many cases surgical intervention is not necessary. However, at present only a few specialised centres are able to offer this treatment (Farese et al., 2004).

Palliative treatments
These have the aim of improving the quality of life of patients with cancer, primarily by relieving the pain, and are not given with a curative intent or to prolong survival.

Radiotherapy is used for this purpose and can reduce pain and lameness. The protocols are based on low doses and a small number of applications with minimal side effects on healthy tissues. The percentage of animals that benefit from this treatment varies between 50% and 90% while the analgesic effect ranges from 53 to 108 days. There are protocols involving two (Ramirez III et al., 1999), three (Bateman et al., 1994; Ramirez III et al., 1999; Mueller et al., 2005) and four (Green et al., 2002) sessions and the so-called accelerated protocols (Knapp-Hoch et al., 2009). It is not clear whether the combination of radiotherapy and chemotherapy can prolong the duration of the analgesia.

In one study it was observed that the survival of dogs with metastatic appendicular osteosarcoma (stage III) was longer among those treated with radiotherapy rather than surgery (Boston et al., 2006).

Bisphosphonates, in the form of zoledronic acid (Spugnini et al., 2009), pamidronate (Fan et al., 2005, 2007, 2009) and alendronate (Tomlin et al., 2000), have been used as bland palliatives of pain.

Some success has been obtained in the local reduction of pain with metronomic chemotherapy based on doxycycline, piroxicam and cyclophosphamide in dogs with metastatic appendicular osteosarcoma (Liptak et al., 2004b).

Finally, it should be remembered that surgery, whether conservative or radical, not associated with chemotherapy must be considered a palliative treatment in the case of appendicular osteosarcoma.

PROGNOSTIC FACTORS

The negative prognostic factors associated with a shorter survival in dogs with appendicular osteosarcoma include young age (Spodnick et al., 1992; Loukopoulos et al., 2007), high pre-treatment levels of alkaline phosphatase in the blood (both total and bone-specific forms of the enzyme) (Ehrhart et al., 1998; Garzotto et al., 2000; Kirpensteijn et al., 2002a), metastatic lymph node spread (Ehrhart et al., 1998; Garzotto et al., 2000; Kirpensteijn et al., 2002a), high histological grade (grade III) (Kirpensteijn et al., 2002a; Loukopoulos et al., 2007), stage III osteosarcoma (metastatic) (Boston et al., 2006), costal, scapular and humeral osteosarcoma (Bergman et al., 1996), high body weight (Hammer et al., 1995; Ru et al., 1998), incomplete excision (Hammer et al., 1995) and tumour size (Misdorp et al., 1979).

COMPARATIVE ONCOLOGY

Canine osteosarcoma is a unique model for studying human osteosarcoma because of the similarities between this malignancy in humans and dogs (Table 3). Comparative oncology is gaining increasing interest since the study of spontaneously occurring neoplasms in pets (dogs and cats) raises new diagnostic and therapeutic possibilities of interest in both human and veterinary medicine (Mueller et al., 2007; Paoloni et al., 2007, 2010; Gordon et al. 2009, 2010).

Table 3. Similarities and differences between appendicular osteosarcoma in dogs and humans.

AXIAL OSTEOSARCOMA

About 24% of osteosarcomas in the dog occur in axial bones. In a study of 116 subjects with axial osteosarcoma (Heyman et al., 1992), 27% of the tumours were located in the mandible, 22% in the maxilla, 15% in vertebrae, 14% in cranial bones, 10% in the ribs, 9% in the nasal cavity and 6% in pelvic bones. There are also reports, albeit rare, of involvement of the penile bone and patella.

VERTEBRAL OSTEOSARCOMA

Vertebral osteosarcomas are rare and are characterized by an aggressive behaviour both locally (lytic lesions) and systemically (high metastatic potential) with affected animals having a survival of 4 months following combined surgery, chemotherapy and radiotherapy (Dernell et al., 2000). Pain tends to prevail over the establishment of true neurological signs.

OSTEOSARCOMA OF THE RIBS

Osteosarcoma is the most frequent tumour of the ribs (28-63% of cases), followed by chondrosarcoma (28-35%). Rare cases of costal fibrosarcoma and haemangiosarcoma have also been reported. Costal osteosarcoma usually develops in elderly, large animals but no breed or gender predilection is known. The most common signs include a palpable mass in the chest wall. Breathing difficulties have been noted in cases with massive extension of the tumour within the thoracic cavity with compression of the heart and lungs or pleural effusion. Lameness of the anterior limb can occur because of mechanical interference or invasion of the brachial plexus by the tumour. In most cases the tumours are found at the costochondral junction, but they can also be located in the sternebrae. Multiple tumours (in several ribs) have been described. Locally the tumours may be lytic (more often), productive or have mixed features. They metastasise above all to the lungs and bone (16%).

The diagnostic work-up is the same as that described for osteosarcomas of the appendicular skeleton. It is worth carrying out X-rays of the tumour to evaluate its extension, the number of ribs involved, and any spread to adjacent structures such as the pericardium, vertebrae, lungs, and X-rays of the chest to determine whether lung metastases are present or not. More accurate information can be obtained through computed tomography (Fig. 11).

Surgical treatment consists of excision of the tumour with a wide margin which must include removal on one rib cranial to the tumour and one caudal to it, 3 cm of macroscopically normal costal bone dorsally and ventrally to the tumour and 3 cm of margins around tissues adjacent to the tumour (pleura, muscles, fascia). Any adhesions with adjacent organs must be excised en bloc  (pulmonary lobectomy, pericardiectomy) rather than debrided. Depending on the extent of the surgical defect, the reconstruction involves the use of autologous muscle flaps or the application of omentum with or without prosthetic mesh implants.

It has been demonstrated that post-operative administration of chemotherapy improves the survival of dogs with costal osteosarcoma, compared with that achieved with surgery alone, passing from 90 days following only surgery to 240-290 days when surgical excision of the tumour and chemotherapy are combined (Dernell et al., 2007; Liptak et al., 2008). The chemotherapeutic drugs are the same as those used in the appendicular forms. Costal osteosarcoma has also been described in the cat.

OSTEOSARCOMA OF THE PELVIS

Pelvic osteosarcoma can cause the onset of lameness and deformities; in rare cases there may be constipation secondary to external compression of the colon/rectum by the tumour mass, which can be palpated both externally and via the rectum. The biological behaviour of pelvic osteosarcoma is the same as that of appendicular osteosarcoma and requires multimodal management (surgery, adjuvant chemotherapy and, in some cases, radiotherapy). Surgery can be used to excise variable amounts of the pelvis up to the point of hemipelvectomy (Straw et al., 1992).

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