Prolymphocytic leukemia (PLL) is a very rare subtype of chronic leukemia. Although most forms of chronic leukemia progress slowly, PPL is often aggressive and can be difficult to treat.

We’ll walk you through what you need to know about PLL, including the symptoms, how it’s diagnosed, current treatment options, and more.

PLL is a rare and aggressive type of chronic leukemia.

The American Cancer Society estimates that more than 60,000 people will receive a diagnosis of leukemia in the United States in 2021.

Less than 1 percent of all people with chronic leukemia have PLL. It’s most often diagnosed in people between ages 65 and 70 and is slightly more common in men than in women.

Like all types of leukemia, PLL affects blood cells. PLL is caused by the overgrowth of cells called lymphocytes. These cells usually help your body fight infection. In PLL, large immature lymphocyte cells called prolymphocytes are produced too quickly and overwhelm the other blood cells.

There are two subtypes of PLL:

  • B-cell prolymphocytic leukemia. Roughly 80 percent of people with PLL have this form. It causes overgrowth of B-cell prolymphocytes.
  • T-cell prolymphocytic leukemia. About 20 percent of people with PLL have this subtype. It causes too many T-cell prolymphocytes to develop.

PLL, like other chronic leukemias, is often found on lab work before any symptoms develop. When symptoms develop, they might include:

There are a few additional symptoms that are specific to T-PLL, which include:

Many of these are general leukemia symptoms and are also found in less serious conditions. The presence of any of these symptoms doesn’t always indicate PLL.

In fact, since PLL is rare, it’s unlikely that it’s causing your symptoms.

However, it’s a good idea to see a healthcare professional if you’ve been experiencing any of these symptoms for more than a week or two.

Because PLL is very rare, it can be hard to diagnose. PLL sometimes develops from existing chronic lymphocytic leukemia (CLL) and is found during lab work when monitoring CLL.

PLL is diagnosed when more than 55 percent of the lymphocytes in your blood sample are prolymphocytes. Blood work can also be checked for antibodies and antigens that can signal PLL.

If PLL isn’t found during routine blood work, a healthcare professional will order more tests if you have symptoms that might indicate PLL. These tests may include:

  • Bone marrow biopsy. A bone marrow biopsy is performed by inserting a needle into a bone (typically the hip) and removing a piece of bone marrow. The sample is then analyzed for prolymphocytes.
  • Imaging tests. Imaging tests such as CT or PET scans can check for an enlarged liver or spleen, which are signs of PLL.

Currently, there’s no one specific treatment for either type of PLL. Your treatment will depend on how fast your PLL progresses, the type you have, your age, and your symptoms.

Since PLL is rare, your doctor will likely come up with a treatment plan specific to your case. Healthcare professionals may often encourage people with PLL to sign up for clinical trials to try new medications.

Treatments you might receive for PLL include:

  • Active surveillance. Active surveillance is also called watchful waiting. It involves your healthcare team monitoring you closely. You’ll start receiving treatment when your blood work shows that PLL is progressing or when you start having symptoms.
  • Chemotherapy. Chemotherapy can be used to try to control PLL progression.
  • Medication. Medications called targeted therapy are used to stop the spread and growth of cancer cells. You might use these on their own or in combination with chemotherapy.
  • Surgery. Surgery to remove the spleen is sometimes an option to improve your blood counts and relieve any pressure that an enlarged spleen might be putting on your other organs.
  • Radiation therapy. Radiation therapy for your spleen is sometimes offered when surgery isn’t an option.
  • Stem cell transplants. People in remission from PLL following a round of chemotherapy might be eligible for a stem cell transplant. A stem cell transplant is the only known cure for PLL.

PLL is an aggressive form of chronic leukemia. Therefore, the outlook is generally poor due to how quickly it may spread. But outcomes and survival rates can vary greatly between people.

As mentioned earlier, one potential cure for PLL is a stem cell transplant, although not all people with PLL are eligible to receive stem cell transplants.

Newer treatments have improved survival rates in recent years, and research into new therapies is ongoing.

PLL is a rare type of chronic leukemia. It’s most commonly diagnosed in people between 65 and 70 years old. It often progresses more quickly and is treatment-resistant than other forms of chronic leukemia.

Treatment options depend on your overall health, age, symptoms, and the type of PLL you have. People are often encouraged to take part in clinical trials to take advantage of new therapies.