Should you take rapamycin if you already have cancer?

Hi Everyone,

My almost 14 year old dog has just been diagnosed with hemangiosarcoma, a common canine cancer. She has been taking rapamycin for almost two years and has led as toxin-free a life as I could manage, home-made, organic food, balanced nutrition, minimal to no medications and vaccines, etc., etc. Everything was supposed to be perfect for her…but here we are.

My question is about the continuation of rapamycin once one has cancer. I know that, overall, once rapa has been in your system for some time, your immune system is strengthened. But there is also that period of the cycle right after you take rapa that suppresses your immune system.

Hemangiosarcoma tumors are the most rapidly growing tumors in the canine world - tumors can spring up and become visible in weeks and the prognosis is usually two days from discovery. My girl is going on week six, which is surprising and superb, but her tumor is inoperable and I am trying to figure out if suppressing her immune system for that beginning part of the rapamycin cycle will give free rein to her tumor growth for those days or, if by continuing to give it to her, I am overall helping her immune system fight the tumor growth with a continuance of its improved vigor that the rapa provides. I am also aware that, having been on rapa for almost two years, discontinuing her will still give her the benefits of the immune strengthening that she gained over that period.

FYI, for now, I opted to discontinue her, but am still pondering the best course of action. And it is certainly a question that may arise in the future for similar situations, although I hope isn’t so…

I am also a patient of Dr. Green and have written him with this question but he has not yet answered me. I know no one might have any experience with such a situation, but, you are a very informed and thoughtful group of people, so I’d appreciate hearing your thoughts.

All my best,



In general when patients are terminal all medication except for the ones for immediate comfort should be stopped. I think rapamycin falls under that category. Unfortunately your dog will die soon, no point in prolonging or adding extra suffering

I had an 11.5 year old golden retriever that I was giving 4mg/week rapamycin to. She had a routine physical where she had a clean bill of health except that she had elevated white blood count. I got scared and discontinued the rapamycin. Six weeks later she developed a 5cm hemangiosarcoma (it was not there at her previous physical) and was told that she had hours to days left. She didn’t seem to be in discomfort so we did not put her down and I started her on 4mg rapamycin 3 times per week. She was fine for a while but I had to put her down 12 weeks later. The vets were astonished that she made it that long. She was in no discomfort but just got more sluggish as time went on.

Rapamycin is currently being investigated when given with other compounds for cancer treatment in dogs.


I believe that Rapamycin would slow the cancer down but not cure it. The anecdotal evidence above supports that theory.


Thank you all for your comments - I have since gotten some answers from vets who confirm that it is helpful to continue rapa with the cancer and I, too, have now seen the studies using rapamycin for cancer - so she is back on it and we are simply enjoying our time together…




You might be interested to read this:

I have no affiliation or connection with this site. I don’t have a dog and know nothing about the illness. But maybe you might want to read it.

Good Luck!