Chronic lymphocytic leukemia (CLL) and prolymphocytic leukemia (PLL) are types of blood cancer. They develop in types of white blood cells called B cells or T cells, or the precursors to these cells.

Leukemia is a group of cancers that develop in the tissues that create blood cells. Leukemia is divided into many subtypes depending on the type of blood cells that become cancerous and other features of the cancer, such as how quickly it progresses.

Chronic lymphocytic leukemia is one of the most common leukemias in adults. “Chronic” means it tends to progress slowly and “lymphocytic” means that it starts in early forms of a type of white blood cells called lymphocytes.

Prolymphocytic leukemia (PLL) is a rare cancer first described as an aggressive form of CLL in the 1970s. PLL develops in mature lymphocytes called prolymphocytes.

PLL was originally divided into B- and T-cell subtypes, but the B-cell form was removed from the 5th Edition of the World Health Organization Classification of Hematolymphoid Tumors. Its cases are now classified under:

  • splenic B-cell lymphoma/leukemia with prominent nucleoli
  • transformations of indolent B-cell lymphomas
  • mantle cell lymphoma

This article examines the differences between CLL and T-cell PLL.

Leukemia symptoms tend to be general and similar to those of many other conditions.

Prolymphocytic leukemia (PLL) symptoms

Symptoms of T-cell PLL include:

Chronic lymphocytic leukemia (CLL) symptoms

CLL symptoms often develop slowly over time and often include:

Leukemia is caused by genetic changes that cause abnormal blood cells to replicate out of control.

Prolymphocytic leukemia causes

T-cell PLL is an extremely rare and usually aggressive cancer. It develops when genetic changes cause mature T cells to replicate out of control. T cells are a type of white blood cell that destroys foreign invaders.

In most cases, T-cell PLL has no obvious cause.

Chronic lymphocytic leukemia causes

Doctors don’t know exactly what causes CLL. Like PLL, it’s caused by genetic mutations that cause lymphocytes to replicate uncontrollably, and it often doesn’t have an obvious cause.

Risk factors for CLL include:

  • age over 50
  • exposure to some chemicals like Agent Orange
  • family history
  • male sex

T-cell PLL is most common in males and older adults. About half of people are diagnosed over the age of 61.

Leukemia symptoms can be difficult to spot. It’s advisable to contact a doctor if you develop potential warning signs, especially if they don’t improve after a couple of weeks. Some of the warning signs can include:

  • swollen lymph nodes
  • unexplained fatigue
  • night sweats
  • unexplained weight loss
  • unexplained fever

General tests doctors perform to start the diagnostic process include:

  • review of your personal and family medical history
  • review of your symptoms
  • physical exam

If your doctor suspects leukemia, they’ll likely order two types of blood tests called a complete blood count and a blood differential test. These tests let doctors see the number of each type of cell in your blood and whether you have too many abnormal or immature blood cells.

Other tests you might receive include:

The main treatments for CLL are:

Learn more about CLL treatment.

T-cell PLL is often widespread when it’s diagnosed. People with T-cell PLL without symptoms are often treated with observation alone, where monthly physical exams and laboratory tests are performed to monitor how the cancer is changing.

Clinical trials with new treatments are often recommended for people with T-cell PLL since the cancer tends to be aggressive. The targeted therapy drug alemtuzumab remains the mainstay therapy. It has a response rate of around 90% and a complete response rate of about 80%.

The 5-year relative survival rate for CLL was about 88.5% in the United States from 2014 to 2020. This means that people with CLL lived at least 5 years 88.5% as often as people without CLL during this period.

CLL is rarely curable, but many people can live years without treatment. Treatment can slow or even stop the progression of your cancer.

T-cell PLL tends to have a much less favorable outlook. Only about half of people with T-cell PLL live longer than 21 months. Some people have a less aggressive variation, which tends to have a better outlook.

Exposure to certain pesticides and herbicides may increase your risk of CLL. Minimizing your exposure to these chemicals may help reduce your risk of CLL.

There’s no known way to prevent T-cell PLL.

Are prolymphocytic leukemia or chronic lymphocytic leukemia curable?

CLL often isn’t considered curable but can often be managed for many years with treatment. T-cell PLL may be curable in some people with intense chemotherapy and a stem cell transplant.

Can CLL turn into PLL or vice versa?

CLL and PLL are now considered distinct diseases and are treated independently.

CLL and PLL are two types of cancer that develop in white blood cells called lymphocytes. PLL was once considered a type of CLL but is now considered a separate disease.

Both conditions often aren’t treatable. People with CLL often live many years without treatment. T-cell PLL tends to be aggressive, but it’s sometimes curable with intense chemotherapy and a stem cell transplant.