Greetings FPC members,
One of the more intensely studied phenomenon in cancer research has been the abscopal effect. As a true believer in SBRT and the abscopal effect, I have faced posters questioning the existence and benefits of the effect via SBRT in treating PCa. But what is the abscopal effect??
From Wikipedia, "The abscopal effect is a hypothesis in the treatment of metastatic cancer whereby shrinkage of untreated tumors occurs concurrently with shrinkage of tumors within the scope of the localized treatment. R.H. Mole proposed the term “abscopal” (‘ab’ - away from, ‘scopus’ - target) in 1953 to refer to effects of ionizing radiation “at a distance from the irradiated volume but within the same organism.”
In a nutshell, localized treatment of tumors results in shrinkage of other tumors that are some distance away from the area of treatment as a result of activation of the immune response. This treatment can be a combination of a check point inhibitor like Keytruda, Yervoy, etc. with or w/o radiation or cryotherapy as well as possibly an infusion of an immune stimulator like GM-CSF or radiation therapy alone.
"Well gee, Fish--with that much going on, then why are we not seeing more cures in PCa??" The answer is that tumors have a way to block some of the immune response through regulatory T cells, avoid detection, and certain genetic factors may also play a role in blocking the response. Consequently, the studies have shown mixed response rates for the abscopal effect--see the article below:
futuremedicine.com/doi/full...
Part of the problem is determining: 1) who will be a responder, 2) ways to ensure a response will occur, and then....3) prolonging that response for a potential cure.
Research is ongoing on determining genetic predisposition to a response. At this point, response rates vary from studies-(refer back to article). In The ORIOLE trial, about 9% of the individuals receiving SBRT showed increased T cell clonality continued at 90 days. So, if the abscopal effect exists in treated patients somewhere between 10-30%, then how do we increase that number and prolong the effect??
That is indeed the issue. Increasing the response percentage and prolonging the immune response generated. Part of it will be sequencing I believe. Determining the proper treatment order that ensures that response and prolongs it... The other is discovering ways (treatments or drugs) to promote and prolong the immune response related to the abscopal effect.
I hope you enjoyed this introduction on the abscopal effect and I look forward to discussion.
Don Pescado
