Dr. Brady Stein explains the diagnostic tests and genetic mutations that are assessed to determine prognosis and what MPN treatment may work best.
Dr. Brady Stein is a hematologist focusing on myeloproliferative neoplasms (MPNs) at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. Learn more about Dr. Stein, here.
Once a patient is diagnosed with MPN, what sort of testing should take place?
So, the test that’s going to lead to suspicion is going to be a blood count, and that’s probably going to be done in the primary care doctor’s office, so that’s going to be the first suspicious test, and in general, there’s going to be some abnormality. Myeloproliferative diseases are characterized in general by an overproduction of blood cells, so it’s going to be a higher white count, it’s going to be a high hemoglobin or hematocrit, or a high platelet count, or a combination of the three that’s generally going to lead to suspicion.
Some patients may have pretty unremarkable blood counts and may present with a blood clot in an unusual location that could ultimately lead to the hematology referral. Some patients might have pretty unremarkable blood counts, but they might have palpation of their spleen, enlargement of their spleen in a physical examination. So, they’re generally the ways that patients are getting to the hematologist.
And, what about bone marrow biopsy?
So, a bone marrow biopsy is a diagnostic test, and it’s generally recommended for all patients who have a myeloproliferative neoplasm either confirmed or suspected.
It’s advised in WHO criteria – World Health Organization criteria. PV can be made without a bone marrow biopsy – a diagnosis of PV – because it’s the most unique of the MPN subtypes. It’s the one that presents with a high hemoglobin.
So, that diagnosis can be straightforward at times for a hematologist when the setting is right, when there’s a high hemoglobin – or, high enough hemoglobin, I should say, a JAK2 mutation, which all patients with PV have that, or a subnormal erythropoietin level.
Oftentimes, we can make that diagnosis without a bone marrow, and the bone marrow becomes more prognostic. ET, a bone marrow is necessary for diagnosis, and myelofibrosis, you can’t make a diagnosis without it.
What do the results of these tests tell us about prognosis and treatment choices?
That’s a good question. The bone marrow can be diagnostic in the setting of ET and myelofibrosis. In the setting of polycythemia vera, it can be more prognostic. In general, when a bone marrow is done, 1). To confirm diagnosis, 2). To assess prognosis, what we’re looking for as prognostic features are generally the degree of fibrosis or scarring.
So, each of the MPNs can have that. Of course, MF is characterized by the most pronounced scarring. It can happen to a more subtle degree in ET and PV. That’s going to be prognostic in the setting of ET or PV. The pathologist will alert us about immature cells called blasts.
We basically never see them at diagnosis in patients with ET or PV. We can see them rise in patients with myelofibrosis at diagnosis or through the course of follow-up. So, that’s prognostic.
All bone marrows generally have a chromosome analysis that’s called cytogenetics, and so, if there’s an abnormality, that can help place the patient’s prognosis into different risk categories.
And then, nowadays, more so in myelofibrosis than any of the others, there are extended panels done. These are called NGS, or next-generation sequencing, kind of looking at mutations in a greater degree of detail.
So, not just what we call main mutations – JAK2, calreticulin, or MPL. These are looking at additional mutations that basically hold prognostic significance.
These are pretty well defined, and I think more important in MF compared to the other subtypes.
Would you explain the driver mutations in MPNs? What are they, and how they – or, what they mean for patients?
So, there’s three of what we call driver mutations, and the most common is JAK2V617F, the next most common is calreticulin, and the least common or most rare is a mutation of MPL, the thrombopoietin receptor. So, the driver gene mutations are the three that we assess to help with diagnosis, and the prevalence varies. In ET, about 60 percent have JAK2, 25 percent have calreticulin, 5 to 10 percent have MPL.
In PV, 99 percent have some type of JAK2 mutation, and in MF, the situation is a lot like ET – 60 percent JAK2, 25 percent calreticulin, about 5 to 10 percent MPL. So, the driver mutations – we think of those as the genetic abnormalities that really drive the disease. They’re the main ones we can test for in a diagnostic setting.
I refer to them as the – to a patient, what I’m describing is you have a car, and the driver mutation is the one that’s sort of driving the car, and it’s doing it somewhat recklessly. It’s in the front seat, driving. And, along the way, the driver can pick up hitchhikers, which we should never do. I refer to those other mutations that are found by NGS as hitchhiker mutations that sit in the back seat, cause trouble, and really shouldn’t be there. They’re not the driver, they’re not fully responsible for the disease, but they can make it a bit worse.