The following is a transcript of select comments from this evenings chat with Dr. Michael Lucroy, author of The No Nonsense Guide to Cancer in Pets …
‹tazziedog› (a veterinarian) asks about the incidence of spinal metastasis. Specifically, what treatment is recommended, and what is the general prognosis is for spinal mets.
‹oncovet› Spinal metastasis do occur in osteosarcoma. About 5% to 10% of dogs will have metastasis at diagnosis. Almost all dogs develop them later. The use of chemotherapy tends to increase the risk for bony metastasis. In the spine, we generally have fewer surgical options, so we go for pain control. That often means radiation therapy in combination with pamidronate or similar bisphosphonate drugs.
‹oncovet› We can also use oral medications (NSAIDS, Tramadol, gabapentin and amantadine) to try and help pain control. But the prognosis is not great with spinal metastasis if we can't get them pain free quickly
‹tazziedog› is also interested in your opinion about metronomics and artemisinin.
‹oncovet› we have, in conjuction with the folks at The Ohio State University, treated some dogs with OSA with doxorubicin and artemisinin. there were no adverse effects observed, but we treated too few cases to draw any conculsions about its effectiveness. I don't believe they have published their work yet.
‹oncovet› as for artemisinin side effects – they are mainly reported to be related to the GI tract: vomiting and diarrhea, so you really can't sort that out from the concurrent chemotherapy drug. Likewise there are not really any specific blood effects to watch for, and it is reported "mild blood work changes" can occur – whatever that means!
‹oncovet› When I was on faculty at Purdue University, we had some ongoing trials with metronomic therapy for urinary bladder cancer. With the current economy, some folks are more interested in metronomics for the relative cost differences. We found the bladder tumors would stay stable for a short while with metronomic therapy and it was very well tolerated. However, there needs to be a lot more work done to figure out the best drugs for metronomic therapy, and in which combinations work best for which cancer types. For a disease like OSA, where the metastatic lesions are highly dependent on new blood vessel growth, metronomic chemotherapy might be found to be useful
‹oncovet› Well done! we have seen some of our patients have stable metastatic lesions with metronomic treatments. with Palladia now available, that is another option to add in to the mix
‹oncovet› as from Palladia's action in mast cell tumors, it also seems to affect new blood vessel growth in other cancer types.
‹jakesmom› I was wondering if oncovet had any experience with using bisphosphonates in OSA dogs?
‹oncovet› jakesmom – yes, we use the bisphosphonate drug, pamidronate, in our OSA patients that are undergoing radiation therapy for palliation in lieu of amputation. It really helps with pain control – and in some cases, our radiologist has been impressed with the return to more normal appearing bone in the radiation field
‹oncovet› jakesmom – yes, we use the bisphosphonate drug, pamidronate, in our OSA patients that are undergoing radiation therapy for palliation in lieu of amputation. It really helps with pain control – and in some cases, our radiologist has been impressed with the return to more normal appearing bone in the radiation field
‹rubyaz› my 8 year old rottwieler was diagnosed with bone cancer and then diagnosed changed to valley fever this continued for 3 months back and forth , have you ever heard of that happening before
‹oncovet› rubyaz – here in the midwest, we don't see valley fever, but when I was in CA, that was a maor consideration. you need the combination of pathology from the bone and serology for coccidiodes immitis to help decide what is going on. I can't recall having gone back and forth on the diagnosis like you describe before. Certainly an 8yo Rottie has a breed risk for OSA
‹YodasMom› Any tips on early detection of osteosarcoma (or any other cancers that could lead to amputation) and/or how to avoid misdiagnosis when a limp firsts starts?
‹oncovet› In any older dog that develops a lameness, and particularly those breeds at risk for OSA, we recommend x-rays as part of the initial diagnostic work up. Starting on NSAIDs (Rimadyl, Deramaxx, Previcox, etc.) will make dogs with arthritis and early bone cancer more comfortable. If bone cancer is there, using NSAIDs first simply delays diagnosis.
‹oncovet› There are differences in x-ray findings between OSA (or other bone tumors) and arthritis. With digital x-rays available in many places these days, it is easier than ever to get a veterinary radiologist's opinion about images.
‹oncovet› If a lesion is found, there are several ways to get a sample for diagnosis, including a fine needle aspirate and using various bone biopsy needles
‹Tazzie› From seeing dogs on this website, I got the impression that the spinal mets were noticed pretty much when it was too late to do anything. Is that often the case?
‹oncovet› Yes, often we find the spinal mets when they are advanced – or in a very bad spot for aggressive treatment. Because of the location, you don't have a lot of time to mess around. If they fracture through a spinal metastasis site, the results can be catastrophic for the dog
‹Tazzie› If subQ mets are found with no apparent or no significant organ involvement (based on chest xrays and ultrasound), do you recommend any type of treatment or chemotherapy drugs different from those used for other forms of OSA mets?
‹oncovet› If we had a dog with only SQ mets, and nothing else demonstrated (I'd want a nuclear bone scan to make sure) if there were only a few, surgery might be a consideration, depending on how long out from diagnosis
‹oncovet› it is a challenge to treat established metastases with chemotherapy
‹oncovet› if the SQ metastases were multiple, electron radiation therapy might also be a consideration
‹dogenergy09› I am a canine massage therapist. Today my client asked me whether her dog (five weeks out from amputation), who just started chemo, would become progressively run down or whether he will bounce back after each treatment
‹oncovet› dogenergy09 – we see many dogs that seem to bounce back just fine between treatments, having only a day or two that is "off" according to the owners. there are some, however, that seem to get progressively more tired throughout treatment. there is no great way to predict which dog will be in which group!
‹ldillon81› wants to know: Is there any difference in the way the cancer spreads (starting from an injury vs. originating from nothing)? She read that cancer can occur at a place where a previous injury has occurred.
‹oncovet› Yes, we can see cancer develop at the site of previous trauma. That is well documented in people, dogs, and cats. The injury can be a broken bone, burn wound, or anything else. However, the way the cancer spreads depends mostly on the type of cancer. We used to think that cancers would either spread through the lymphatic system to the lymph nodes or through the blood stream and end up in the lungs, liver, brain etc. But now, we understand that cancer cells can leave the primary tumor and enter both the lymphatic system and the bloodstream at the same time. Where cancer starts to grow depends on the type of tumor and the patient's immune system.
‹dogenergy09› In your experience have you encountered cases of bone cancer stemming from the metal plate in a TPLO?
‹oncovet› dogenergy09 – I have seen a few primary bone tumors develop at the site of implants (not all OSA and only one TPLO plate that I can recall). It is unclear whether this is related to the presence of the implant, the previous surgical (or other trauma), or something unrelated – like breed risk.
‹dogenergy09› Thanks. I come across this argument from time to time when people are considering options for ruptured ccls and I wondered what the data really show
‹oncovet› 20+ years ago, the bone plates were of low quality and actually would create small electrical charges and corrode, which was thought to be responsible for cancer risk at implant sites. However the modern plates are very well made with almost no impurities, so the risk factors for cancer at those sites is now different.
‹jakesmom› I also have a 5yr old german shepherd. Is he also at risk, or not for a few more years?
‹oncovet› Jakesmom – certainly a GSD is the right size for being at risk for OSA – but the peak incidence of OSA in dogs occurs at 7-9 years…there is a smaller peak at 18-24 months.
‹admin› it seems like pups are being afflicted with cancer at much earlier ages these days, any thoughts?
‹oncovet› we are seeing a lot of young dogs with cancer in our practice – mainly lymphoma and mast cell tumors, but not a lot of ostesarcoma. For youngsters (I'm talking 6 month old puppies with lymphoma) I think the risks could either be genetic, or due to some exposure the dam had during gestation
‹wyattraydawg› What constitutes "exposure"?
‹oncovet› For exposure I mean chemical or nutritional risk factor for cancer development. Mainly what is studied in the field of epigenetics. That is the information that is a second layer contained within the genome…namely methylation of DNA.
‹oncovet› If DNA groups get a lot of methyl groups stuck to them, and they are in the promoter region of a gene, the gene is silenced…that is good for an oncogene
‹oncovet› but the gene silencing is bad if it is a tumor suppressor gene – likewise for losing methyl groups. Nutrition and chemicals affect DNA methylation. Just google epigenetics and you'll find weeks worth of reading material!
‹rockyandme› Why do some vets amputate a fore leg right at the joint and others leave a small "nub"? Do you have a preference?
‹oncovet› rockyandme – in our practice, our surgeons always do what is known as a forequarter amputation – that is they take everything from the scapula on down. This is my preference because it is faster for the surgeons, so less anesthesia time for my patients.
‹oncovet› Also it leaves a much nice appearance, especially in short haired dogs. It is also more comfortable for them – the muscle surrounding the nub with atrophy and the underlying bone looses its cushion
‹FeartheEars› Different with a rear leg amputation?
‹admin› any thoughts on the hemipelvectomy?
‹oncovet› As long as the stump is not bothering the dog, we leave it be. If it becomes a problem, it is pretty straightfoward to modify the amputation to the forequarter
‹jakesmom› What do you mean by 'faster'? Jake had his right foreleg amputated at his joint, leaving his scapula… It was a 3 hour surgery from start to finish…
‹oncovet› My bias for the rear leg is the same – but in this case, removing the entire leg is harder for the surgeons. If the tumor is in the femur – the entire leg always comes off. If it is in the tibia, then I defer to the surgeons and they do a high mid-shaft amputation. There is a ton of musle over the bone so usually they do OK.
‹oncovet› Jakesmom – for our surgeons, a forequarter amputation usually takes about 75-85 minutes – longer for very large size dogs or those that are obese. However, they do a lot of amputations so it is somewhat routine.
‹Tazzie› You said: "the presence of the primary tumor seems to inhibit the growth of metastatic lesions." What are the implications of that? Try to maintain the leg with the primary tumor for longer via radiation and bisphosphonates rather than amputate right away?
‹oncovet› Tazzie – That comment stems from a study done years ago at Purdue. They looked at urine from dogs with OSA – it contained angiostatin, a compound that inhibits blood vessel growth. They rechecked the urine of dogs after amputation and there was no detectable angiostatin. This was done initially to try and help us understand why dogs presented with very large primary tumors and no mets…
‹oncovet› yet mets develop very quickly after amputation if nothing else is done. So, our view is that these results would lead us to pursue antiangiogenic control of the tumor before amputation, or radiation/pamidronate. We see metastasis quickly develop after radiation/pamidronate if no chemotherapy is given, because we are effectively killing the primary tumor.
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