Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in adults in Western countries. “Chronic” means that it tends to develop slowly. “Lymphocytic” means it develops in white blood cells called lymphocytes.

Small lymphocytic lymphoma (SLL) is another name for the same disease. “CLL” is used when most cancer cells are found in your blood and bone marrow. “SLL” is used when most cancer cells are in your lymph nodes.

In the United States, about 5.9 of 100,00 males and 3.3 of 100,000 females develop CLL or SLL a year. CLL and SLL are treated the same and generally have a good outlook with a 5-year relative survival rate of 87.5 percent.

Keep reading to learn more about how CLL and SLL compare and how they’re treated.

CLL and SLL are slow-growing cancers that develop in white blood cells called lymphocytes. More specifically, they develop in abnormal B cell lymphocytes. The function of B cells is to produce special proteins called antibodies. These antibodies attach to foreign substances and tell other immune cells to destroy them.

CLL and SLL are essentially the same diseases. Doctors choose a name based on where most cancer cells are found. Both conditions are treated in the same way, no matter which name they go by.

SLL is commonly used when most cancer cells appear in lymph nodes, and CLL when found in the blood or bone marrow. Bone marrow is the spongy tissue where blood cells are produced inside your bones.

A doctor will typically diagnose either CLL or SLL but not both. Here’s a look at how they compare:

Feature CLL SLL
Where most cancer cells are found Blood or bone marrow Lymph nodes
Monoclonal lymphocyte cell count in blood More than 5,000/mm3 Less than 5,000/mm3

SLL is classified as a type of non-Hodgkin’s lymphoma. Many doctors classify CLL as a type of non-Hodgkin’s lymphomas as well.

What causes CLL/SLL?

Researchers don’t exactly know why some people develop CLL or SLL. It’s thought that genetic factors are primarily responsible. Exposure to Agent Orange and possibly exposure to certain other herbicides and pesticides may also play a role.

Many different genetic mutations in the DNA of blood-producing cells have been identified in people with CLL or SLL. A loss of part of chromosome 13 is the most common genetic mutation that’s been identified.

CLL and SLL are slow-growing cancers that lead to the overproduction of abnormal B lymphocytes. The development of CLL and SLL are the same, and cancer cells are indistinguishable under a microscope.

Usually, CLL represents the initial phase where cells are isolated to the blood and bone marrow. CLL may progress to SLL if cancerous cells spread primarily to lymph nodes.

About Richter’s syndrome

CLL and SLL can also develop into an aggressive form of non-Hodgkin’s lymphoma called Richter’s syndrome. Richter’s syndrome develops in 3 to 15 percent of people with CLL or SLL.

The outlook for Richter’s syndrome is generally poor. Usual symptoms of Richter’s syndrome include:

  • increased lymph node swelling
  • increased swelling in the spleen or liver
  • high fever
  • abdominal pain
  • even more weight loss
  • poorer blood cell counts

Your medical team can help you determine the best treatment for CLL or SLL. The best treatment for you depends on factors such as:

  • your blood cell counts
  • whether you have swelling in your liver, spleen, or lymph nodes
  • your age and overall health
  • your symptoms
  • how you respond to initial treatment
  • whether cancer returns after treatment

Treatments options for CLL and SLL include:

CLL and SLL aren’t usually considered curable, but many people live with these conditions for a long time. The distinction between CLL and SLL doesn’t influence the outlook of the disease.

Half of the people with CLL or SLL live at least 10 years, while some live 20 years or more without treatment.

The relative 5-year relative survival rate is estimated at 87.5 percent. The relative 5-year survival rate compares how many people with the disease are alive after 5 years compared to people without the disease.

Your doctor can give you the best idea about what to expect. Statistics can give you an idea about your outlook, but many factors can determine how you’ll respond to treatment.

Factors that influence outlook

Factors that can influence your outlook include:

  • whether you have a certain gene mutation such as TP53or IgVH
  • your blood cell counts
  • the stage of your cancer
  • results of tests such as beta-2 microglobulin test
  • your age and overall health
  • how quickly cancerous cells drop during treatment
  • whether you develop a second cancer

CLL and SLL refer to the same type of blood cancer that develops in a type of white blood cell called lymphocytes. CLL is generally used when most cancer cells are in your blood or bone marrow. SLL is used when most cancer cells are found in lymph nodes.

CLL and SLL are treated the same way. The distinction doesn’t influence your treatment plan. Your medical team can help you determine how to best manage your condition.