Hairy cell leukemia: 6 questions, answered

Hairy cell leukemia is a rare blood cancer diagnosed in only about 1,000 people each year in the United States. Usually slow-growing, it’s considered a chronic form of leukemia. That means it involves mature cells: in this case, a type of white blood cell called B cells. 

To learn more about how hairy cell leukemia is diagnosed, what symptoms to look for, and how it’s treated, we checked in with leukemia specialist Farhad Ravandi, M.D.  

How did hairy cell leukemia get its name?

It comes from the appearance of the diseased cells. There are small projections all over them that resemble hairs, so they look very much like a child’s drawing of the sun. 

How is hairy cell leukemia typically diagnosed? 

In the past, patients would often come to their doctors with enlarged spleens. But today, we normally don’t see that too much. Now, it’s typically found through low blood counts during routine lab work.  

What are the most common symptoms of hairy cell leukemia?

Many people don’t have any symptoms at all. So, patients could have it for years before they’re finally diagnosed. When people do have symptoms, they might include: 

• extreme fatigue 
• night sweats
• weight loss
• feeling full quickly, even after eating just a small amount of food 

How is hairy cell leukemia typically treated?

There’s been an evolution in therapy for hairy cell leukemia over the past 50 years.  

In the 1960s and 70s, surgeons would typically just remove the spleen. That would improve things, but only for a short while, because it didn’t address the underlying problem.  

In the 1980s, interferon became the standard of care for a while. But it was not very curative.  

In the 1990s, the chemotherapy drugs cladribine and pentostatin were developed. Both proved effective against hairy cell leukemia, with many publications reporting an 80% to 100% response rate among patients who received them. Eventually, cladribine became the standard.

Then, in the late 1990s and early 2000s, rituximab came along. This targeted therapy drug was already being used extensively against lymphoma and other lymphoid leukemias. Since hairy cell leukemia has the highest expression of the specific protein being targeted by that drug among all leukemias and lymphomas, naturally, scientists wanted to test it out on that, too. 

Rituximab proved to be very effective against hairy cell leukemia, even as a single agent. So, we developed a combination of it and cladribine here at MD Anderson. That’s what we’ve been using ever since. It’s a big success story in leukemia treatment.  

Patients who’ve received the combination of cladribine and rituximab here at MD Anderson have had a 100% response rate, with rare relapses over the past 18 years. About 40% of patients who receive cladribine alone will relapse within four or five years. So, patients have a much better response when cladribine and rituximab are combined. 

What’s on the horizon in hairy cell leukemia treatment?

We already have a totally effective regimen with the combination of cladribine and rituximab. But it’s nice to have options.  

That’s why we took note around 2010, when a group of Italian researchers discovered that the BRAF mutation is almost always indicative of hairy cell leukemia in lymphoid malignancies. That same mutation occurs frequently with melanoma, so that discovery gave us a lot of insight into the biology of both diseases. 

Vemurafumib and dabrafenib are two targeted therapy drugs that were already approved by the Food and Drug Administration (FDA) for the treatment of BRAF-driven melanomas. They’re not approved yet for use with hairy cell leukemia, but we’re investigating them in patients who’ve relapsed through clinical trials.  

Another targeted therapy drug called ibrutinib is also being studied for hairy cell leukemia treatment. The FDA has already approved it to treat chronic lymphocytic leukemia. Other drugs being developed for lymphoid diseases are likely to be effective against hairy cell as well. 

What’s the one thing you want people to know about hairy cell leukemia?

We don’t just jump into treating every patient with hairy cell leukemia. Specific criteria must be met first. A patient has to already have a lot of what we call constitutional symptoms, such as night sweats and fatigue.  

Patients also have to have a significant lowering of blood counts, and the values have to fall below a certain level. I have some patients who didn’t start treatment for two or three years after diagnosis, or even longer. 

In these cases, we monitor patients very closely, and we’re able to offer a highly effective option when they need to start treatment. 

Request an appointment at MD Anderson online or by calling 1-877-632-6789.