Both chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) refer to the same disease. The name depends on where the cancer cells are concentrated.

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. Doctors diagnose CLL when most cancer cells are found in your blood and bone marrow and SLL when most cancer cells are in your lymph nodes.

In the United States, about 5.8 per 100,000 males and 3.3 per 100,000 females develop CLL or SLL a year. CLL and SLL are treated the same. People who receive a diagnosis of these cancers generally have a good outlook with a 5-year relative survival rate of 87.7%.

Keep reading to learn more about how CLL and SLL compare and how doctors treat them.

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 disease. Doctors diagnose one or the other based on where they find the most cancer cells. But they treat both conditions the same way.

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

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

FeatureCLLSLL
where most cancer cells are foundblood or bone marrowlymph nodes
monoclonal lymphocyte cell count in bloodminimally 5,000/mm3less 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 lymphoma as well.

Researchers do not exactly know why some people develop CLL or SLL. Researchers believe genetic factors are primarily responsible. But environmental factors may also play a role. This may include:

  • exposure to Agent Orange
  • exposure to certain other herbicides and pesticides
  • tobacco use and exposure to cigarette smoke
  • exposure to high amounts of radiation

Different genetic mutations in the DNA of blood-producing cells have been identified in people with CLL or SLL. This typically includes a loss of part of the following chromosomes:

  • chromosome 13, the most common
  • chromosome 17
  • chromosome 11

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 3–15% of people with CLL.

The outlook for people with a Richter’s syndrome diagnosis 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
  • increased weight loss
  • poorer blood cell counts

Your medical team can help you determine the best treatment for your CLL or SLL. This 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

Treatment 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 does not influence the outlook of the disease.

The median survival rate with CLL or SLL is at least 10 years, while some people whose cancer presented at stage 0–II, per the Rai staging system, live 20 years or more without treatment.

The relative 5-year relative survival rate is estimated at 87.7% based on people receiving a diagnosis between 2013 and 2019. 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 specifically 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 the beta-2 microglobulin test
  • your age and overall health
  • how quickly cancerous cells drop during treatment
  • whether you develop a second cancer

How is CLL different from SLL?

Doctors diagnose CLL when most cancer cells are found in your blood and bone marrow and diagnose SLL when most cancer cells are in your lymph nodes. If you have CLL, you have more than 5,000/mm3 monoclonal lymphocytes in your blood.

What is the difference between CLL and SLL staging?

CLL and SLL are staged and treated the same way.

What is life expectancy with CLL or SLL?

Many with CLL or SLL live at least 10 years, while some people live 20 years or more without treatment. The relative 5-year survival rate is 87.7% and refers to the percentage of people with the disease who are alive after 5 years compared to people without the disease.

When does SLL become CLL?

CLL can progress to SLL if the cancerous cells spread primarily to your lymph nodes.

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 does not influence your treatment plan.

Your medical team can help you determine how to best manage your condition.