SLL and CLL are both lymphocytic conditions that affect the immune system. However, they affect different areas of the immune system.

Both conditions are types of non-Hodgkin lymphoma. These cancers start in the white blood cells and affect the lymphatic system.

SLL: Lymph nodes

In people with SLL, cancer cells appear mainly in the lymph nodes.

The lymph nodes are small bean-shaped glands that contain white blood cells, or lymphocytes, and help filter substances that travel through the lymphatic fluid. Lymph nodes are part of the body's immune system.

CLL: Bone marrow and blood cells

CLL also affects the immune system. However, in CLL, the cancer cells appear mainly in the bone marrow and blood cells. Bone marrow is the spongy tissue in the middle of the bones that makes substances that produce blood cells.

Cellular differences

When doctors examine the cancer cells under a microscope, both SLL and CLL look the same. However, there are some differences in the blood.

A person with CLL will have more than 5,000 monoclonal lymphocytes per cubic millimeter (mm$^3$) in the blood. A person with SLL will have less than 5,000 monoclonal lymphocytes per cubic millimeter (mm$^3$) in the blood, but they will also have a swollen spleen or swollen glands.

The cancers are so similar, so many of the same treatments are used for both SLL and CLL.