Chronic lymphocytic leukaemia (CLL) and small lymphocytic lymphoma (SLL) are cancers that affect B cells, a type of white blood cell that forms in the bone marrow. CLL and SLL are treated as the same disease. When most of the cancer cells are found in the bloodstream and the bone marrow, the disease is referred to as CLL (although the lymph nodes and spleen can often be involved). When the cancer cells are mostly located in the lymph nodes, the disease is called SLL.

CLL/SLL is typically a slow growing leukaemia with a long disease course. However, like all cancers, each patient experience is unique. While CLL/SLL is a relatively uncommon type of cancer, it is the most commonly diagnosed type of leukaemia or blood cancer, with approximately 1500 new cases diagnosed every year in Australia. Most people with CLL/SLL are around 70 years old when they are diagnosed, while diagnosis under 40 years is considered rare. CLL/SLL typically affects men more than women.

The symptoms associated with CLL/SLL relate to the overproduction of cancerous B cells in the bone marrow. B cells form in the bone marrow, which is located deep inside your bones, and are released into the bloodstream to help the body fight off infections. B cells pass through the lymphatic system, which includes the lymph nodes and spleen. With CLL/SLL, too many abnormal and dysfunctional B cells are created, which crowd out other healthy cells made in the bone marrow, like red blood cells and platelets. This is what can lead to symptoms like feeling tired or getting sick more often.