PRRT--What is it and how does it work?
/Peptide Receptor Radiotherapy (PRRT, sometimes known as PRRNT or Peptide Receptor RadioNuclideTherapy) is an internal radioactive treatment for Neuroendocrine Tumors. Internal radiation therapy is nothing new; people use it for bone tumors, prostate tumors, and others. But there's something special about PRRT and NETs. Remember, these neuroendocrine tumors have something called the Somatostatin Receptor (SSTR). It's the target on the tumor we can attack. We use a somatostatin analogue (octreotide) to get the radiation to the tumor.
Think of it this way, we use regular octreotide (cold) as a biological treatment to tell the tumors to quiet down. We use the 68-Gallium labelled octreotide to take pictures of the tumors. We use the PRRT labelled octreotide to carry a "bomb" and treat the tumors.
PRRT was developed by the Europeans, specifically the Dutch. Dr. Eric Krenning has been working on this therapy for over twenty years. They started treating people well over ten years ago and their trial suggests that it is an effective treatment. They describe people having stable disease for about four years.
Now, there are things to consider. It's NOT A CURE. It's a treatment. The most important thing is that your octreoscan or 68-Gallium scan must be positive. Your tumors must have the receptor/target on them for this to work. If there's no SSTR, then there's no target for the PRRT to bind to.
Another point is that there are two types of "radioactive payloads" that can be attached to the octreotide peptide. 177Lutetium is more widely used, is the second generation isotope, and is better tolerated. 90Yttrium is also used, it was the first generation and carries more energy. In general 90Y has more side effects so limits the number of treatments you can get. 177Lu is usually 4-6 treatments, whereas 90Y is usually two. The major toxicities are damage to the bone marrow (blood counts) and the kidneys. Luckily both are generally pretty well tolerated. It's usually the blood counts that cause people to stop treatment.
You might hear about different types of peptides - they are all somatostatin analogues. DOTA is the part that binds to the isotope (Ga, Lu, Y) like a cage. Then the suffix -TATE, -TOC, -NOC, describe the type of peptide. Minor differences because they all work essentially the same.
Unfortunately, it is not widely available here in the U.S. It's mostly in Europe. And it's pretty expensive. If you go to Europe, the treatment is probably around $15,000 x 4 treatments for a total of $60,000. It's a little different from place to place, but it's something like that. That doesn't include airfare and hotel.
For some neuroendocrine cancer patients, it really is a life-saving therapy. For others, it just doesn't work. So, always talk with your NET expert and explore if PRRT is a viable treatment for your disease.
We are excited because there are next-generation peptides coming out. Something people are excited about is a molecule called JR-11 from a German company called, Octreopharm. It is supposed to bind much more strongly, so we are hopeful. In the meantime, a French company called Advanced Accelerator Applications is testing the more traditional PRRT 177-Lu-DOTATATE (a.k.a. Lutathera) and are very far along. We'll keep our fingers crossed.
If you want more information, take a look at PRRTinfo.org. It's run by Josh Mailman (NorCal CarciNET) and Gary Murfin (Board member Healing NET Foundation). They describe their experience going to Bad Berka, Germany and getting treatment with Dr. Richard Baum. You can also check out several patient stories on their site. http://prrtinfo.org/patient-stories However, there are other places (see the map on PRRTinfo.org).
Eric Liu, M.D.
Neuroendocrine Specialist
