Platelet levels as an indication for cytoreductive treatment in ET

Dr Chris Hillis is an assistant professor in the Division of Oncology at McMaster University and hematologist at the Juravinski Hospital and Cancer Centre.

Is a very high platelet number (>1-1.5 million/microL) an indication for cytoreductive treatment in patients with essential thrombocythemia (ET)?

Chris Hillis, MD, MSc: Certainly it starts to get a bit scary as the platelets go above 1 million, 1.5 million, or 2 million. In and of itself in an otherwise healthy person, who has no other indication for cytoreduction, we may actually not begin cytoreduction at 1 million. Most guidelines would say that 1.5 million would be the indication for treatment, but really it is on a case-by-case basis.

I think the most important thing to remember as the platelet count starts to get around 1 million and above is to check for acquired von Willebrand syndrome. Many of these patients will be on aspirin and it may be no longer safe to continue to give them aspirin if they do develop acquired von Willebrand syndrome. You may then start cytoreduction, follow up the von Willebrand [factor] levels, and then resume aspirin when it is safe to do so.

What about symptoms like headache? Are they related to this platelet count?

Typically yes. As patients with ET start to develop more symptoms, I do wonder about transformation and I start to look at other aspects on the blood film that may give a hint that the person is transforming to myelofibrosis. But it is very difficult to treat the constitutional symptoms or symptoms like headache, dizziness, or light-headedness with cytoreduction. I find in about 50% of patients that they do get better, but the other 50% unfortunately do not. Unlike when you are controlling hematocrit and polycythemia vera (PV) and you will start to get a symptomatic improvement, I do not find the same in all patients with ET.