Mike B:

Hello, I’m being treated for chronic lymphocytic leukemia and polycythemia. My question is how many people in the United States have both of these? Thank you.

Dr. Aaron Gerds:

Hi. Well, thank you so much for your question. Absolute pleasure to try to answer it the best I can. And this is a question we get a lot. We do see a lot of patients in the clinic who have both a myeloid neoplasia like polycythemia vera (PV), as well as lymphoid neoplasia, like lymphoma or CLL (chronic lymphocytic leukemia), in your case.

And trying to link the two is certainly an area of active interest. The biology of what we think is going on is that there’s some sort of primordial stem cell issue where one of the bone marrow stem cells is predisposed or predestined or has some sort of abnormality, where it splits off abnormal clones over time. And some of those clones can be myeloid, like PV cells, and some of those clones might be lymphoid, like a CLL cell.

There’s probably some sort of ancestral stem cell that’s slightly abnormal, not to the point where we can detect it necessarily very readily, but some sort of abnormal stem cell that’s spitting off these abnormal clones. Thus, increasing the risk that you have a second hematologic issue. First, in your case, the PV and then the CLL.

And how often does this occur? Well, there’s been a couple of studies that have tried to address this. There was a really nice study published back in 2018, from a European country, where they looked at the whole population of the country. So, they are able to get all the people in the country and look at this large population-based database.

They looked at over 9,000 patients with MPN (myeloproliferative neoplasms) and did see that the risk of developing a lymphoid disease after your myeloid disease was increased. So, they didn’t really get down in the granular of different types of lymphoid disease, they just had lymphoma. But it did look like the risk of lymphoma was higher for people that had an MPN versus those who did not.

Here in the United States, we have a large national database of cancer called SEER (Surveillance, Epidemiology, and End Results). So, it’s a large maintain database of patients diagnosed in the United States with cancers in general.  Andrew Brunner along with colleagues like Gabriela Hobbs, Donna Neuberg and Amir Fathi did a nice paper that was published back in 2016, looking at this very question.

They use this database, and in this database, they have identified over 20,000 patients with MPNs. They looked at those patients with MPNs, to see how many of them developed other cancers. And then, if they did develop other cancers, what is that risk compared to the normal population?

Certainly, patients with PV can develop CLL. But so, can people who don’t have PV and is there a clear difference between people who have PV and don’t have PV and the numbers of folks who get ultimately CLL at some point?

Well, they did in this database of over 20,000 MPN patients find some that also developed CLL. In fact, they found 33 patients who developed a second cancer, that was CLL. The incidence of this database and of these patients in this database, at five years is about .2 and at 10 years, it was .3, so again, not terribly common.

But when you compare people who have PV in this database, PV, myelofibrosis, essential thrombocythemia, the MPNs. So, people in this database were versus people who don’t have an MPN, there was an increased risk of developing CLL.

And we use this measure called incidence ratio, where we take the chances or the probability of getting CLL in one group and compare it to the probability of the other. So, it was increased, it was about two and a half times the normal incidence rate.

So again, circumstantial evidence, but certainly pointing to the direction of what we think biologically is going on that there is some sort of primordial cell in the bone marrow, that is predisposed to spinning off multiple hematologic clones, like a PV cell, and then maybe a CLL cell in the future. Thus, explaining the increased risk of developing CLL in patients with PV.

Now I want to point out that out of the 20,000 patients with MPNs that were looked at only 33 had CLL. So, this is not a very common occurrence. I would not recommend that all patients with MPNs go and get screened for CLL or have CLL type testing done. But we do know that it is an increased risk. If we do see someone with an MPN, who has a very elevated lymphocyte count, we would want to go and examine whether or not those lymphocytes are in fact CLL.

So again, not something that’s very, very common, but there is some data to point out that it kind of clarifies how common it is. And try to identify the risks of patients who have MPNs for developing second malignancies like CLL. So that data does exist and again it’s a question we get a lot in the clinic and one I’m happy to help answer today.