Hairy cell leukemia-variant is an extremely rare and unique type of leukemia (cancer) that was once grouped with another type but is now considered a separate condition.

Leukemia is a form of cancer that affects your blood cells, bone marrow, and other related tissues. It often prevents your white blood cells from working correctly. Healthy white blood cells come in many types that all work together to help fight infections and disease.

One rare form of leukemia is hairy cell leukemia (HCL), named for the hair-like filaments found on affected white blood cells. It’s sometimes called “classic” HCL. Only about 2% of leukemia diagnoses are HCL.

Hairy cell leukemia-variant (HCL-V) was once thought to be a form of HCL but is now viewed as a distinct condition. It’s only about one-tenth as common as HCL, making it a very uncommon condition.

Let’s take a look at the basics of HCL-V and how it’s different from other types of leukemia.

Your bone marrow contains blood stem cells. These cells can turn into either a myeloid stem cell or a lymphoid stem cell.

Myeloid stem cells mature into red blood cells, platelets, or one of many types of white blood cell called granulocytes. Leukemias affecting these cells are called myeloid leukemias.

Lymphoid stem cells can mature into other types of white stem cells, such as B cells (and further into plasma cells), T cells, and natural killer cells. Leukemias affecting these cells are called lymphocytic leukemias.

HCL-V affects B cells, so it’s classified as a chronic lymphocytic leukemia (CLL). It’s a chronic form of leukemia, meaning it’s typically a more slowly developing form of the disease.

The exact causes of CLLs aren’t known, but experts believe that genetic changes — called mutations — can cause your B cells to multiply too often.

Some of the known risk factors for CLL include:

  • age over 50
  • exposure to radon or Agent Orange
  • close relatives (parents, siblings, or children) with CLL
  • race/ethnicity from North America or Europe

The symptoms of HCL-V are the same as the symptoms of classic HCL.

Because HCL-V is often a chronic condition, you might notice the symptoms slowly over time, or may even have no symptoms at all.

Common symptoms of HCL-V include:

  • swollen abdomen
  • pain or fullness in your abdomen
  • frequent infections
  • feeling tired or weak
  • shortness of breath
  • bruising or bleeding

These symptoms can be caused by many conditions. If you have these symptoms, it doesn’t necessarily mean you have HCL-V or even cancer. Only a healthcare professional can say for certain, so if you’re experiencing these symptoms, be sure to meet with a doctor for an evaluation.

If a doctor suspects you have HCL-V, you’ll probably have a few different tests performed in order to find out for sure.

You can expect to have one or more blood tests which might include a bone marrow aspiration or biopsy. Your samples will be sent to a lab to be analyzed.

The lab will look at what types of cells are in your blood, their shapes, and their relative quantities. They’ll also check for foreign substances — called antigens — and genetic changes. The differentiating factor of antigens between HCL-V and classic HCL can be seen by using a flow cytometry test. This is the main method of differentiating HCL-V from classic HCL.

You might also have an ultrasound or CT scan performed to check if your spleen or lymph nodes are swollen.

Because HCL-V is rare and was only recently classified as a distinct disease, there isn’t an established treatment plan for HCL-V.

The genetic differences between HCL-V and classic HCL mean that the treatments for one don’t usually work very well for the other.

One therapy that may be used is cladribine chemotherapy followed by a monoclonal antibody medication called rituximab. When used correctly, the rate of remission is close to 90%, according to one 2018 review.

Experts recommend that treatment should only start after you begin to experience symptoms, with regular evaluations by a doctor every 3 to 6 months.

Some people with HCL-V might need to have a splenectomy, which is a surgery to remove your spleen.

Other treatments, such as ibrutinib (Imbruvica), are still being studied. If you have HCL-V, you might consider joining a clinical trial.

According to a study from 2012, the overall 5-year survival rate for people with HCL-V is about 57%. There are many factors that can significantly affect the outcomes from person to person, and some people with HCL-V have been able to experience remission.

Be sure to discuss your outlook with a doctor at the time of diagnosis.

What is a 5-year survival rate?

Health professionals often use the 5-year survival rate as a measure of your outlook. This rate refers to the percentage of people with the disease that are still alive at least 5 years after their diagnosis.

Another commonly used term is “5-year relative survival rate.” This is a measure of how many people with the disease are alive 5 years later compared with people without the disease.

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Having HCL-V can take not only a physical toll but also an emotional one. In the coming months or years, you might find it helpful to prioritize your physical tasks and monitor your mental health.

Eating a balanced diet, getting enough sleep, and exercising to your level of ability can all contribute to maximizing your energy level. You might consider asking a family member or close friend for assistance as needed with tasks like getting to and from your treatment appointments.

There are also support groups available for both you and your family. You might consider finding a local group through the Leukemia & Lymphoma Society or another organization.

You might be looking for some basic facts regarding HCL-V. Here are some common questions that people have.

What is the difference between classic and variant hairy cell leukemia?

Classic HCL and HCL-V are genetically distinct.

In classic HCL, there’s usually a mutation on the BRAF V600E gene, but this mutation isn’t there for people with HCL-V. Instead, HCL-V typically has a mutation on the MAP2K1 gene.

This can lead to the diseases behaving differently. For example, people with HCL often have monocytopenia as a symptom, whereas people with HCL-V usually don’t.

For this reason, classic HCL treatments that target the mutated BRAF V600E gene don’t work as a treatment for HCL-V.

How long can you live with hairy cell leukemia-variant?

There’s no cure for HCL-V, but it’s possible to treat it.

Sometimes treatment can lead to complete remission, meaning that all the symptoms and indicators of cancer are gone. It’s still possible for cancer return after being in remission.

You can live a typical life span with HCL-V, but this will depend on how your body responds to treatment.

HCL-V is a distinct form of chronic lymphocytic leukemia. It has important genetic differences that distinguish it from classic HCL.

This is a very rare disease. There are some treatment options available, but you might also want to speak with a doctor about joining a clinical trial.