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Do I need to take a bone biopsy?
Why not do an FNA? Fine needle aspiration of bone lesions can be an effective way of demonstrating cancer cells and this is often all the information you need to decide the first step in treatment (surgery in most cases). The precise tumour type (e.g. chondrosarcoma versus osteosarcoma) is usually less important at this stage, but knowing whether the lesion is inflammatory or neoplastic is key.
To get a good cell harvest with an FNA of a bone you need a very different aspirate technique to that for a lymph node however. Try the following and see what you think :
• Use a long 21g needle with 10ml syringe attached
• Insert into the middle of the lesion and apply 5-10mls negative pressure.
• Move the needle back and fore / re-angle it several times, keeping negative pressure applied.
• Release negative pressure immediately before withdrawal of the needle.
• You will get a lot of blood with this method, but also a decent yield of neoplastic cells, so make at least 10 slides, and stain 1-2 in-house and check to make sure you have caught cells other than blood / inflammation before sending them off.
• This technique is cheaper, and quicker than a bone biopsy, and avoids the risk of pathologic fracture!
If the radiologic findings convincingly demonstrate an aggressive bone lesion with an unstable cortex, isn’t it a waste of the client’s money to pursue a diagnosis before amputation?
The successful treatment of most osteolytic cancers will hinge around local control of the tumour, and in many cases this will involve limb amputation. Nevertheless histiocytic sarcoma is a notable exception where hypofractionated radiation therapy produces great results, returning most cases rapidly to full weight-bearing very effectively. The dog’s breed and the anatomic location of the lesion may affect the suspicion of this particular malignancy versus osteosarcoma. Cytology should be adequate for diagnosis of a histiocytic sarcoma (or even rarer bone tumours for example lymphoma or plasma cell tumours which can sometimes be treated medically).
Do I really need to x-ray the chest ?
Although metastasis at the time of osteosarcoma diagnosis is uncommon (less than 20%), the presence of gross pulmonary metastasis will significantly reduce the prognosis for canine osteosarcoma from approximately 10-14 months to approximately 3 months. The client may find this staging information useful in deciding whether to proceed with surgery and chemotherapy.
Additionally, a number of bone tumours are in fact metastatic lesions (for example urogenital carcinomas), or part of a systemic disease process (for example multiple myeloma, haemangiosarcoma or lymphoma). Staging information is therefore very helpful before proceeding with amputation.
Should the dog have an orthopaedic assessment before amputation?
In many cases, dogs will have been effectively 3-legged for the last few weeks due to non-weight-bearing lameness, so the ability to cope on 3 legs will have already been demonstrated. However, it is always prudent to consider the orthopaedic function of the remaining limbs before an irreversible amputation surgery, and in these increasingly-litigious times we should document that we have done this. Particularly where chronic orthopaedic disease exists or is suspected assessment from by an orthopaedic surgeon may be very helpful.
Is limb-sparing surgery the gold-standard ?
Limb-sparing surgery has its’ place, but it’s not appropriate for every case. Currently, the procedure is only suitable for distal radial tumours, with a small tumour size and minimal involvement of soft tissues. Sadly many bone tumours are diagnosed at other locations or at a more advanced stage. The majority of dogs receiving limb-sparing operations (regardless of technique) have a high rate of complications for example infection and implant failure. Dogs with (much rarer) scapula tumours or ulna tumours can do very well simply with scapulectomy or ulnectomy however, and this is a much simpler limb-sparing technique.
If I know it’s a cancer do I need to send the amputated leg for histo?
For the tumours which are treated with amputation, post-operative chemotherapy is indicated in some diagnoses (for example osteosarcoma), but may not be for others (for example chondrosarcoma). And for those where chemo is indicated, the drugs used and protocol will differ depending on the diagnosis. So, for prognostic and therapeutic purposes then, obtaining the diagnosis is vital!
“I’d go for surgery, but I wouldn’t put him through chemo…”
This attitude is understandably held by a number of clients, but their perception is ill-founded! Chemotherapy in dogs (in particular the treatments used for osteosarcoma) will be associated with a normal quality of life throughout treatment; side effects will either be absent, or mild and self-limiting. Therefore we need to educate our clients that side effects of chemo will be no more likely or no more severe than treatment for many other chronic medical conditions, and is often “putting him through” much less than surgery!
What does the adjuvant chemotherapy involve?
The standard-of-care adjuvant chemotherapy treatments would either be carboplatin or doxorubicin, single-agent, given intravenously. Neither drug has been found to be superior, and an alternating protocol has shown no benefit. Since carboplatin is cheaper, and has fewer potential side effects, this drug is used as single-agent most commonly. Carboplatin is typically given as a short, intravenous infusion, every 21-28 days.
Carboplatin can cause acute nausea and so premedication with maropitant (oral or IV) is necessary. Providing anti-nausea medication is given, gastrointestinal adverse effects are very rare. The point of maximal myelosuppression can be very variable with this drug however, and delayed neutropaenias (and thrombocytopaenias) are infrequently recognised. Rather than checking for neutropaenia 7 days after the drug is given, 2 blood tests at 10 days and 14 days is more commonly practiced. Once the nadir has been established as “safe” the author does not perform further nadir checks after subsequent injections. Carboplatin can cause nephrotoxicity (although it is much less nephrotoxic than its sister drug, cisplatin!) and so it is advisable to check kidney function before each dose, and consideration should be given to administration of the drug in running saline.
Client refuses surgery. Is there any benefit of just medical treatment ?
This situation is always a concern. Osteolytic lesions are extremely painful, and care has to be taken to preserve the dog’s welfare. The stoic nature of many dogs may lead clients to erroneously believe that their pets are not as painful as they actually are. If the client opts for palliative treatment, palliative-intent radiation therapy (often involving 1 dose, once weekly for 3-4 weeks at most centres) is the most analgesic treatment we can consider and all RT centres will be happy to provide this. Osteoclast inhibitors (for example pamidronate or zoledronate, given by intravenous infusion every few weeks), are also very analgesic and can be used with or without radiation therapy. Systemic analgesics should be used in all cases but even a combination of a non-steroidal drug, tramadol and gabapentin are unlikely to be adequate on their own. With radiation therapy and a combination of medical analgesics, the average survival time is in the order of 5-6 months.
What about bone tumours in cats ?
Aggressive bone lesions in cats can look deceptively non-aggressive radiographically, underlining the importance to sample osteolytic lesions in this species. Care has to be taken since Mycobacterial disease can be an important differential diagnosis!
Primary bone tumours in cats are rare, but 67-90% are malignancies. Approximately 70-80% of the malignant lesions are osteosarcomas, with fibrosarcoma, chondrosarcoma and haemangiosarcoma making up the bulk of the remainder. Osteosarcomas in cats are much less aggressive than those in dogs, with fewer than 10% being reported to metastasize. Osteosarcomas of the appendicular skeleton are often cured with limb amputation however those of the axial skeleton have a reported median survival time in the order of 7 months; in many cases this is due to the difficulty of adequate local control rather than any inherent difference in the biology of the disease in the axial skeleton. Adjunctive chemotherapy in cats is not indicated after adequate local control.
