In my last two posts about osteosarcoma (OSA), we discussed treatments that address the tumor affecting the bone. We discussed amputation, Stereotactic RadioSurgery (SRS) like Cyberknife, palliative radiation, and limb-spare surgery.
While these treatments are important for the malignant tumor destroying the bone, metastasis (cancer spread) is inevitable. So even if the primary tumor is successfully removed with surgery or killed with SRS, these tiny metastases (which are often undetectable at first) will grow and eventually kill dogs with OSA. This makes systemic treatments aimed at controlling micrometastasis a critical part of conventional care.
Chemotherapy Delays Metastasis
I know what you are thinking: chemo for your dog sounds scary and crazy. But overall chemo in dogs is very well tolerated, with minimal side effects. It’s one of the things I like about my job! Hospitalization from chemo-induced side effects is rare. I have a whole series of blogs dedicated to chemotherapy and its side effects, so if you haven’t read them, check them out. The pet Guardians of my patients are always amazed how healthy and happy their pets are during and after chemo.
I bring this up again because chemotherapy is very effective for OSA to delay metastasis. When compared to treating with amputation alone, chemo more than doubles median survival times:
- Survival times for OSA cases with amputation and no other treatment have a median survival time of four to five months, with 90-100% dying by one year, and only 2% still alive at two years.
- Median survival times for OSA cases with amputation and chemotherapy increase to ten to twelve months, with 20-25% of dogs are still alive at two years.
For me and many of my patients, those odds make chemotherapy a no-brainer.
Which Chemotherapy Protocol Works Best?
The most common chemotherapy drugs are doxorubicin, carboplatin, and cisplatin, which you can read about more in the Guide. The published protocols vary on which drugs to use, how frequent treatments should be, and the number of treatments. Consulting with an experienced oncologist who can look at your dog’s own case and weigh all the options that would work best for him or her is your best bet.
At my recent annual Vet Cancer Society conference in the fall of 2012, there was a great abstract from the group at Colorado State University which looked at almost 500 dogs to compare protocols. Dogs either received doxorubicin, carboplatin, or a protocol that alternated the two. Based on this preliminary report, there were no significant differences in the protocols when measuring how long the patients remained tumor-free, and survival times. As always the case with research abstracts, we will need to wait for the published protocol to come out, but at this point, one protocol does not appear to be better than the other. So discuss the different drugs with your oncologist, with regards to your dog’s specific needs.
Doxorubicin and CyberKnife or Stereotactic Radiation Surgery
A word about using chemotherapy with CyberKnife treatments: for my CyberKnife cases, we don’t use doxorubicin. We avoid this specific drug in cases that have received SRS, because there is a side effect called radiation-recall. This chemotherapy protocol, when given after radiation, can bring back or “recall” some of the early skin side effects that you normally see in the first few weeks after radiation – skin side effects such as redness and burning. (You may hear your oncologist call this “moist desquamation.”) If a dog receives doxorubicin, even months later, those skin side effects can recur. So I never use doxorubicin after CyberKnife, and instead use carboplatin.
The best time to start chemotherapy is soon after surgery or radiation, before metastasis has been detected. I typically start chemo about two weeks after surgery or SRS.
Bottom Line: You Have Time
While a diagnosis of OSA may be very scary, it is not an immediate death sentence. As you’ve seen, there is a wide variety of treatment options. As always, I encourage you to consult with an oncologist and discuss the pros and cons, based on your dog’s underlying health, the extent of the disease at diagnosis, and your budget.
All the Best
Sue Ettinger, DVM. Dip. ACVIM (Oncology). Dr. Sue is a boarded veterinary medical cancer specialist. As a Diplomate of the American College of Veterinary Internal Medicine (Oncology), she is one of approximately 400 board-certified veterinary specialists in medical oncology in North America. She is a book author, radio co-host, and an advocate of early cancer detection and raising cancer awareness. Along with Dr. Demian Dressler, Dr. Sue is the co-author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity.