So, PRRT is one of the accepted modes of technique which are used to treat Neuroendocrine Tumors.
But, how do you determine whether PRRT is the treatment of choice for your condition?
So, whenever we talk about neuroendocrine tumors, why are they called Neuroendocrine Tumors because their cell of origin is from the Neuroectodermal Cells and they have these tumors have certain endocrine functions which means they secrete certain hormones which cause some symptoms in the body depending on the kind of hormones which has been secreted.
So, the neuro endocrine tumors can arise from any organ of the body. The decision whether to treat a patient with PRRT or not depends on a few things. The most important thing is:
- Where is the Origin of the Tumor?
- What is the Aggressiveness or the Proliferation of the Tumor?
- Is the tumor progressive or is it kind of stable, so how aggressively is it growing? And
- and probably the most important is that does it express the receptors which are used to treat or to target the PRRT.
So, coming to the first point the typical sites from which a Neuroendocrine Tumor will arise are from the thymus, from the lungs, from the pancreas, from the stomach, from the intestines, from the upper part of the intestines which is small intestines which is the jejunum or ileum and from the lower part of the intestines which is the distal part which is the rectum.
So, these are the typically the sites from which Neuroendocrine Tumor will grow and although they can grow from anywhere these are the sites which often are the patients who go in for PRRT for therapy.
Now, out of all the sites the lung and the pancreas are probably the more aggressive tumors as compare to the small intestine and the rectum, which, while has a tendency to spread to the liver much more than the lung tumors, usually has a more indolent course
- Where is the site of the disease?
- What is the proliferation of the tumor?
So, if you look at your histopathology report you will find something called a Ki-67 or a Mib Index now the Ki-67 or Mib Index actually says how aggressively this tumor is growing. If the Ki-67 is less than 20%, then if it is less than 2% then it is a grade one tumor, if it is between 2%-20% then it is grade two tumor, if it is more than 20% or more than 30 % now according to the newer guidelines then it is a grade three tumor and there are certain more varieties of Neuroendocrine Tumors which are the poorly differentiator or Un-Differentiator or what we call as Neuroendocrine Carcinomas. N ow typically PRRT is used for grade two tumors which means that the Mib Index or the Ki-67 should be between about 2% - 30%.
The third point is - how aggressively is it growing? It is important because these tumors are often indolent it is important to establish that this tumor is either progressing so it is growing and there are new sites of disease that is the intent to treat, that is a time when one should actually think of using PRRT if the tumor is fairly stable patient is asymptomatic then we can wait and watch. Whether these tumors are expressing the receptors which are used for actually targeting the molecular therapy which PRRT entails that is evident from a scan which is called a Gallium Dotanoc Scan or which is called a Octreotide PET CT you can have different kinds of PET CT’s you can have a Gallium 68 Dotanoc whole body scan which is a PET Scan which is specifically for Neuroendocrine Tumors you can also have some Technetium Hynic-TOC Scan which also looks at the receptors. So the important thing here is to establish and to document that the tumor is showing a good receptor expressions so that we have the target to actually treat these patients. There are studies which also do a regular FDG PET CT because a regular FDG PET CT actually tells you whether the tumor is very aggressive or not. It also has some prognostic factors where by a tumor which is positive on FDG PET CT scan is less lightly to benefit from PRRT.
So, there is again, you have to compare the two studies, one Somatostatin Receptors or Octreotide Scan vs FDG Scan. If we find that the Octreotide Scan shows better expression, then the patient goes in for PRRT. If the FDG Scan shows higher avidity of FDG, then the patient goes for Chemotherapy. So, the important things in deciding whether to go in for PRRT or not is that the tumor should be progressive, it should have a Low Proliferation Index and it should express the Somatostatin Receptors with a lot of avidity as compared to the regular FDG Scan.