The Basics of Hairy Cell Leukemia



Kristie L. Kahl: In simple terms, can you explain what hairy cell leukemia is?

Dr. Leslie Andritsos: Hairy cell leukemia is a very unique, rare type of leukemia that is a cancer of a specific type of B cell, which is a mature B cell for reasons that we don't always understand. These B cells can acquire mutations that cause them to grow when they're not supposed to be growing and it may be actually be more than one mutation. And so what we find is that the hairy cells start to involve the bone marrow, spleen and possibly other parts of the body, and eventually can cause problems.

The complications of hairy cell leukemia are actually very similar to other types of similar lymphomas. It is important to emphasize that even though it's called a leukemia, it's actually a type of lymphoproliferative disorder. So, it is very important to differentiate exactly what type of lymphoproliferative disorder this is because it makes a huge impact on the type of treatment that is chosen.

Essentially, when we're trying to figure this out, although some patients may have hairy cells circulating in their bloodstream, that's not actually most common. Most of the time, if it's suspected that a person has a type of blood cancer, we do need to perform a bone marrow biopsy. So, we will look at the blood counts but it's very important to look at the bone marrow biopsy and see what's going on in there. And there are specific panels of tests that are run on the bone marrow that look at the appearance of the cells that are infiltrating the bone marrow, and also specific testing for the proteins that are on the surfaces of the cells, because, for hairy cell leukemia, it is a very unique profile of proteins on the outside of the cell that are detected. If a very specific combination of proteins are present it is very likely to be hairy cell leukemia and it helps to rule out other types of lymphoproliferative disorders; for example,splenic marginal zone lymphomas and others that can actually have hairy cell projections.

The way hairy cell leukemia gets its name is when, initially, scientists were looking at these cells under the microscope, they have these hair-like projections that are very unique and distinct but actually other lymphomas and lymphoproliferative disorders may have a similar appearance.

So once you have the information about what type of proteins are on the outside of the cell and also what mutations are present, because the majority if not all of patients with classical hairy cell leukemia will have BRAF V600E mutations. If the mutation is present and the right type of proteins are present, it's usually very clear that the diagnosis is hairy cell leukemia. There is

another type of hairy cell leukemia that is called variant hairy cell leukemia and it is really important to differentiate these two because the treatment is different variant hairy cell leukemia tends to behave more aggressively and you don't want to mix up the two. Variant hairy cell leukemia usually does not have a BRAF V600E mutation and it's also missing some of those proteins on the outside of the cell.

So, most of the time the diagnosis is pretty straightforward. If it turns out that the diagnosis is not straightforward that might be the time for actually a specialty pathologist such as a hematopathologist to review the case.

Kristie L. Kahl: What is the rate of hairy cell leukemia diagnoses in the US each year?

Dr. Leslie Andritsos: Hairy cell leukemia makes up about 2% of all leukemias so it's pretty rare. There are only about 600 to 800 new cases of hairy cell leukemia diagnosed in the U.S. per year, although I will say, because the survival has improved so much over the past few decades, many more people are living with hairy cell leukemia than there were originally.

Kristie L. Kahl: What are the signs and symptoms of hairy cell leukemia?

Dr. Leslie Andritsos: Historically, most people, when they would present with hairy cell leukemia, would have a serious infection and come to the doctor's office or get admitted to the hospital with a serious infection and then be identified to have usually low blood counts and a large spleen. Those are two hallmarks of the disease. Nowadays, we're finding that people are diagnosed very early in the course of their illness because they go for their annual physical exam and routine blood work and are found to have low blood counts. That kind of starts the investigation as to what's going on. So, some people are diagnosed a little bit earlier in the course of their disease.

The symptoms of hairy cell leukemia may include, obviously, the symptoms of infection; abdominal discomfort; difficulty eating a full meal, which we call early satiety which indicates that the spleen is so large that it's starting to press on the stomach and cause problems;patients may have bleeding from low platelet counts; infections from low neutrophil counts;and also there is a sort of general immunocompromise that comes from a feature of classic hairy cell leukemia, which is low monocyte counts which, nobody really understands why that happens but it does increase the risk of infection. Some patients may just have overwhelming fatigue that takes them to their doctor's office for an evaluation.

Kristie L. Kahl: What is the rate of relapsed or refractory disease occurring?

Dr. Leslie Andritsos: Unfortunately, we don't have a cure yet for hairy cell leukemia but some people will stay in remission for a very long time, sometimes over 10 years, depending on how good their remission was with their therapy. So, we sort of feel that about 40% of people will eventually relapse but that percent is probably higher in people who were diagnosed when they were very young, so they live longer with the disease and and may have an increased risk of relapsing just because they are living with it for a longer period of time.

Kristie L. Kahl: With the disease being on the rare side, why is there an urgent need for more research and more awareness?

Dr. Leslie Andritsos: Because this is a rare disease, there's a lot that we don't know about it. We don't have a cure for hairy cell leukemia, but we know that it's a highly treatable disease. When when this disease was first identified many years ago, there was not effective therapy and the average survival was about only four or five years. Since a few key clinical trials were performed, the average survival is now identical to unaffected persons. So people with hairy cell leukemia can have the same survival as if they did not have hairy cell leukemia. So that shows the impact of therapeutic clinical trials that can identify new treatments that can really have an impact on the natural history of the disease.

Kristie L. Kahl: What is the key thing patients with HCL should know about their disease?

Dr. Leslie Andritsos: They should know that it is a serious illness. Many times, early on in their disease, they get diagnosed with hairy cell leukemia and people know that the outcomes with treatments now, in some cases, are very good. And so they get told that they have a “good leukemia” but from my perspective there is no good leukemia, especially when it's something that you'll be living with the rest of your life and can have plenty of complications, not just from treatment but from the disease itself. So I think it's important to find a doctor that you're comfortable with, somebody with some expertise in the disease to inform yourself about your disease and what are the important things.

I think understanding your own blood counts is very important and knowing how to interpret where you're at with your disease and what is your risk of complications because if you're someone that has a low neutrophil count from your treatment or just from the disease, you really need to go to the hospital. If you get a fever and there's certain key elements, that can be really critical for successful outcomes in hairy cell leukemia.

Organizations like the Hairy Cell Leukemia Foundation that can provide answers and connect with somebody that can help manage problems or side effects and also connect with other patients that can be sort of like peer mentors to help them through their disease and kind of give them some pointers on managing side effects and things like that can be very helpful, especially in a rare disease where you may never meet somebody else with it and outside of an organization that can bring you together. It can be a very isolating experience.

Transcription edited for clarity.

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