I go into the vet tomorrow for Ellie's 2nd carboplatin treatment.  She elected to do 4 stating that there is has been no difference in survival rated between 4 and 6 treatments.  I'll ask her which study(s) to see if I can pass them on to you.

I emailed my oncologist and she referenced the 2014 study that the link Jerry shared is referring to.  I have a copy of the study if you'd like it. She also sent this response, which I appreciated.

"Hi Whitney,

Kara passed your question along to me- I am one of the medical oncologists at CSU and oversee our oncology clinical trials program. Your question is a great one, and one that we all have had as veterinary oncologists. The main study that we quote to say that there is no difference in outcome for dogs receiving 4 vs 6 doses of carboplatin was a study published out of CSU about 9 years ago, and I am attaching a copy of this paper for your reference. The main goal of this study was to look at differences in outcomes and side effects for dogs with osteosarcoma treated with carboplatin or another drug, called doxorubicin, which is also commonly used to treat dogs with this disease. This was a retrospective study, meaning the patients had already been treated when the data were collected, and all of the data were obtained from the medical records of these patients. Because of this, there were some dogs included that had received a 4 dose protocol and others a 6 dose protocol of carboplatin. The study did not find any differences in outcomes for dogs treated with 4 vs 6 doses of carboplatin or carboplatin vs doxorubicin. This was quite a large study (470 dogs), but given that it is retrospective, it does not provide as high of a level of evidence as a prospective trial would. Unfortunately, the fact is that most of the research that is published in veterinary medicine is retrospective in nature, so it can sometimes make it tough to interpret the results. The other problem with this is that we will often see conflicting results with retrospective studies (i.e. one paper may say there is no difference between 4 and 6 doses and another may find something different), which can make it tough to know if there is any true difference.

From a clinical trials perspective, there is a specific reason we treat dogs with osteosarcoma that are enrolled in clinical trials that use carboplatin with four doses. That is because there was a prospective clinical trial conducted a few years ago that enrolled 324 dogs with osteosarcoma from multiple different hospitals that compared dogs that received amputation followed by 4 doses of carboplatin to dogs that received this same treatment plus another drug. One of the goals of this study was to provide prospectively collected information about dogs treated with what is considered to the standard of care for comparison for future trials. That way, when we do clinical trials like the one in which Ellie is participating, we have a reference population to which we can compare our results.

Hopefully this helps to answer your question. I apologize if any of it is confusing, and I’d be happy to speak with you about this at Ellie’s visit tomorrow if you would like. The one thing I can promise you is that we would not be doing this trial as it is designed if we thought that there was a clear benefit to 6 doses of carboplatin over 4. I hope Ellie is doing well, and we look forward to seeing both of you tomorrow!

Take care,

Kristen Weishaar, DVM, MS, DACVIM (Oncology)

Director of Clinical Trials

Flint Animal Cancer Center

Colorado State University"