Harry Erba, MD, PhD: This has been a great discussion on myelofibrosis and polycythemia vera. There are clearly new agents that have recently been approved and are being investigated. Let’s come to something that the clinician out there is going to see, where there hasn’t been as much activity and that’s in essential thrombocythemia. I want to turn to Mary Frances to lead off our discussion on how these patients present and how do you risk stratify them.

Mary Frances McMullin, MD: Again, these are often an incidental finding—somebody who has a blood count done for some time and then finds to have a high platelet count and is sent for investigation. Often, in those patients when you look back at their previous blood counts, their platelets have been up for a long period of time. They may present with symptomatology, but it’s nonspecific. Very often they’ve had the blood count done because they’re complaining of being tired or something like that. Obviously, then, the patients present with a thrombotic event of some sort. For most of them it’s the blood count that they have done that leads to their referral.

Harry Erba, MD, PhD: Robyn, do we always have to treat these patients?

Robyn Scherber, MD: No. For lower-risk patients, especially patients who have age less than 60, with no prior history of thrombosis, and who don’t smoke and really don’t have cardiac risk factors, observation is generally recommended to be something that’s worth considering. I do like to put all patients without a contraindication on aspirin therapy, 81 mg daily, and watch their blood counts still.

There are the results of the PT-1 [primary thrombocythemia-1] study—Mary Frances, you were involved in it and Claire Harrison was involved in that—looked at the intermediate-risk patient, so patients who might have 1 of those risk factors. In those, they looked at cytoreductive therapy, but what they didn’t really see is that there was much benefit to cytoreductive therapy. They didn’t see a significant decrease or change in thrombotic risk. For those patients who maybe just carry 1 risk factor, it is worth considering again just observing. Certainly, once they carry 2 or more risk factors, that’s when I really start to think that cytoreduction would be a good option. I do monitor symptoms again. I think this is key. Some of the most common symptoms I see in ET [essential thrombocythemia] that can be severe and maybe not something we’re routinely asking for other than just fatigue is headaches and itching as well in this population.

John Mascarenhas, MD: Just to be provocative, because I like to be, we know that the height of the platelet count does not predict thrombotic risk. One of the problems I always have with this discussion—I have it every time I treat a patient—is what is our goal platelet count? What are we trying to achieve? What’s our readout for success in treating patients with cytoreductive therapy? Because I would even argue there’s a meta-analysis that would suggest that giving aspirin in a calreticulin low-risk ET patient probably affords no benefit at all. I think we often overtreat these patients without a clear role. It’s a very frustrating thing as an MPN [myeloproliferative neoplasms] physician.

Robyn Scherber, MD: That’s another great thing I didn’t mention. Knowing the mutational status of the driver mutation of MPN is key in ET because we do know that those CALR type 1 mutations really do tend to be lower risk. Certainly, I think it’s worth considering. Even patients, if they do carry maybe 1 high-risk factor in a CALR mutation, they may not need to be treated again.

Harry Erba, MD, PhD: OK, I’m going to come back to that.

Transcript Edited for Clarity