Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are both types of non-Hodgkin lymphoma that affect the lymphocytes. Lymphocytes are a type of white blood cell.

Both cancers are so similar that healthcare professionals often group them as CLL/SLL. Due to the similarity between the two conditions, there is no difference in how doctors approach their treatment.

This article discusses the differences between CLL and SLL and breaks down the similarities between the two.

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Both CLL and SLL are types of indolent non-Hodgkin lymphoma. This means that they are slowly spreading cancers that start in white blood cells and affect the lymphatic system.

The lymphatic system is a network that is part of both the circulatory and immune systems. It transports a watery fluid called lymph throughout the body. The lymph contains white blood cells, among other things.

According to the National Cancer Institute, CLL and SLL both cause immature white blood cells to affect the immune system and are the same condition. The main difference is the part of the immune system the cancer affects.

Different locations

If a person has CLL, cancer cells appear mainly in the blood and bone marrow. The bone marrow is the spongy tissue on the inside of bones. This tissue plays a role in producing blood cells.

If a person has SLL, the cancer cells affect primarily the lymph nodes. The lymph nodes are glands that filter out waste and contain white blood cells. They help the immune system protect the body against infection.

Cellular differences

The cancer cells in CLL and SLL look the same under a microscope.

However, a person with CLL will have more than 5,000 monoclonal lymphocytes per cubic millimeter (mm³) in the blood, and someone with SLL will have less than 5,000 monoclonal lymphocytes per mm³.

CLL is the most common type of leukemia in adults, accounting for 7% of new diagnoses of non-Hodgkin lymphoma.

Combined, the rate of new cases of CLL and SLL is 4.6 per 100,000 males and females per year. Moreover, the number of new cases was falling at a rate of 1.8% between 2009 and 2018.

CLL/SLL affects primarily older adults. The median age of people receiving a diagnosis is 68 years.

In 50–75% of newly diagnosed cases, a person will have no symptoms. It can take several years before a person experiences symptoms related to cancer.

When the cancer begins to cause symptoms, a person may experience the following:

People with SLL may also notice swollen glands in the neck, groin, or armpits.

Learn about CLL and stomach pain here.

Both CLL and SLL progress slowly. It can take several years for symptoms to show up.

Doctors and researchers in the United States typically follow the Rai staging system, which classifies CLL into five stages:

  • Stage 0: There is an increased white blood cell count and near-normal red blood cell and platelet counts but no enlargement of the lymph nodes, spleen, or liver.
  • Stage 1: There is an increased white blood cell count but near-normal red blood cell and platelet counts and enlarged lymph nodes.
  • Stage 2: There is an increased white blood cell count but near-normal red blood cell and platelet counts. There is also an enlarged spleen and possibly an enlarged liver and lymph nodes.
  • Stage 3: There is an increased white blood cell count with low red blood cell count and normal platelets. The lymph nodes, spleen, and liver may or may not be enlarged.
  • Stage 4: There is an increased white blood cell count with low or almost normal red blood cell count and low platelets. The lymph nodes, spleen, and liver are enlarged.

Learn about CLL and lymphocyte counts here.

Treatment for SLL and CLL is identical. However, there may be some differences depending on several factors, such as:

  • a person’s age
  • their overall health
  • their symptoms
  • stage of the cancer

A doctor may recommend several treatment options, including:

A doctor may recommend additional treatment options for complications of the cancer. This can include antibiotics to fight infections, and additional treatment to address symptoms such as fatigue.

There is no cure for either SLL or CLL. However, treatment can help improve a person’s quality of life and slow the progression of the cancer.

The cancer slowly progresses over the course of several years. Early stages or asymptomatic cases do not require treatment.

Once symptoms start, a doctor will typically speak with a person about the best treatment options for them. Treatment may help extend their life span and treat symptoms.

Learn about survival rates for CLL here.

Studies and several organizations, including the Lymphoma Research Foundation, indicate that SLL and CLL are two manifestations of the same cancer. The main difference is where the cancer develops and presents.

As a result, doctors will typically classify the cancer as either SLL or CLL, not both.

CLL and SLL are two different manifestations of the same cancer. They share symptoms, potential causes, and treatments.

However, they differ in the areas they affect. CLL affects primarily the blood, while SLL typically affects the lymph nodes.

Treatment can vary depending on the person’s overall health and age and the stage of the cancer. With treatment, individuals may be able to live a long and overall healthy life.