CLL (chronic lymphocytic leukemia) and SLL (small lymphocytic lymphoma) are two forms of the same illness and they are treated in the same way.

If you have SLL, the information included in this application will also apply to your illness. Both forms (SLL and CLL) will be described together as ‘CLL’ unless there is something unique to SLL that is important to highlight.

CLL and SLL are cancers of the blood and lymphatic systems. The lymphatic system defends the body against infection and circulates and regulates fluid levels in the body.

Lymphocytes are a type of white blood cell and are a major part of the lymphatic system. Together with other cells of the immune system, they work to fight infection and prevent disease.

CLL occurs when there is damage to the genes of developing lymphocytes in the bone marrow. This damage changes the normal lifespan of the lymphocytes and they do not die as planned. The increasing number of CLL cells in the blood and bone marrow crowd out healthy blood cells. This can disrupt the ability of the healthy blood cells to carry out their regular functions. Abnormal lymphocytes do not fight infections like healthy lymphocytes do.

Although it is called leukemia, CLL is a type of blood cancer called lymphoma. Thinking of CLL as a lymphoma is important, because CLL behaves and is treated like other indolent (slow-growing) lymphomas.

The difference between CLL and SLL is where the cancer cells collect. When most of the cancer cells are in the blood stream and the bone marrow, it is called CLL. When the cancer cells are mostly found in the lymph nodes, it is called SLL.

CLL usually progress slowly. In many cases, it causes few, if any problems in its early stages. Many people have CLL that is slow growing and they may have stable disease for years with few or no symptoms. Other people with CLL have a faster-growing form of the disease that may cause more symptoms and need treatment sooner.

To learn more about CLL & SLL, please download our patient resource manual: Understanding CLL & SLL: A Patient Guide to Chronic Lymphocytic Leukemia & Small Lymphocytic Lymphoma