Rationale for Switching Polycythemia Therapy

Prithviraj Bose, MD:Management of adverse effects of hydroxyurea is an issue because it’s not infrequent that patients complain of significant fatigue, mouth sores, hair loss, and nausea. In my experience, those tend to be the more common ones, and then you read about leg ulcers. You occasionally see it, leg ulcers, and nonmelanoma skin cancers, etc. I’ve never actually seen hydroxyurea-induced fever, although that can also occur. These definitely could be a reason to switch the patient to ruxolitinib, and that is what I usually do when I come across something that I feel is true intolerance to hydroxyurea, something that the patient cannot really deal with long term. I will go ahead and switch those patients to ruxolitinib.

The indication to switch a patient from hydroxyurea to ruxolitinib is actually varied. You can have intolerance, which is intuitively easier to recognize because it’s just things that the patient tells you and they don’t want to be on hydroxyurea. But then there’s also resistance, and that’s where it gets a little tricky and you run into some gray zones. There is an ELN [elastin] definition of resistance to hydroxyurea, which is a nice framework but probably not something that can be followed to a T. They require 3 months of at least 2 grams a day of hydroxyurea and failure to control blood counts, or phlebotomy requirements, or splenomegaly at that dose for that duration.

But as I just mentioned earlier, not many patients can tolerate 2 grams a day of hydroxyurea, so I think a more reasonable way to frame it is at whatever dose the patient can tolerate. There are those things that tell you that this is not controlling their disease adequately, or you could be seeing persistent leukocytosis. Everything else is controlled, but you’ve got a persistent leukocytosis, a persistent thrombocytosis. Of these, the leukocytosis is more serious because we know that there is a correlation of that with thrombotic risk and worse survival. So one has to carefully evaluate these factors on an ongoing basis. And there are also data that patients who are truly resistant to hydroxyurea have worse survival and higher rates of leukemic transformation. So it’s actually a big deal that needs to not be missed.

Polycythemia vera, like the other classic myeloproliferative neoplasms, is driven by the Jak-STAT signaling pathway. Virtually all patients have an activating mutation inJAK2, and this is what is driving their disease, driving at least the proliferative aspects of their disease. So it’s fairly straightforward to understand why JAK inhibition would work in a disease like PV [polycythemia vera]. And of course, we have randomized trials, the RESPONSE trial and the RESPONSE-2 trial, that really led to the approval of ruxolitinib in the second-line setting in the US and around the world.

Transcript edited for clarity.

Case: 58-Year-Old Woman Diagnosed With Polycythemia Vera

November 2018

• A 58-year old woman presents to PCP complaining of abdominal pain, dizziness and headaches
• PE: BP 140/85; Splenomegaly ~6 cm below left costal margin
• PMH: No prior history of thrombosis
• Lab values:
  • HGB: 17.1 g/dL
  • Hct: .50 L/L
  • RBC: 71 x 10¹²/L
  • WBC: 13.2 x 10⁹/L
  • Serum EPO: 4.1 mU/mL
• Bone Marrow Biopsy: Erythroid hyperplasia
• Cytogenetics: JAK-V617Fmutation