Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are both cancers of the blood. You may hear your care team use both names or even say they are “the same disease.” That can be confusing, though. How can one condition be both leukemia and lymphoma?
A closer look at CLL and SLL
CLL and SLL are two forms of the same cancer; their primary difference is related to the location of the cancerous lymphocytes (which are the abnormal white blood cells multiplying uncontrollably to cause the disease).
Both CLL and SLL affect a type of white blood cell called a B lymphocyte (B cell). These cells are part of a normal immune system and typically help to fight infections. In CLL/SLL, some B cells become abnormal and start to grow and survive longer than they should. Over time, these abnormal cells build up and crowd out healthy cells.
- CLL (chronic lymphocytic leukemia): the cancer cells are mainly found in the blood and bone marrow.
- SLL (small lymphocytic lymphoma): the same cancer cells are mainly found in the lymph nodes or other lymphatic tissues (such as the spleen).
Under a microscope—and at the genetic and molecular level—the cancer cells in CLL and SLL look and behave the same. Because of this, the World Health Organization classifies them together as CLL/SLL. The key difference is simply location:
- If most cancer cells are circulating in the blood, your care team will refer to it as CLL
- If most cancer cells are in lymph nodes and not much in the blood, it’s SLL
Can you have a CLL and SLL diagnosis?
Your doctor might say: “You have CLL/SLL.” And that’s because they’re describing one disease that can show up in different places. In fact, it’s possible to have both CLL and SLL at the same time. For example, a patient might have abnormal cells in their blood and at the same time experience enlarged lymph nodes or an enlarged spleen. Similarly, someone diagnosed with SLL may later have rising numbers of cancer cells in their blood and meet criteria for CLL. This overlap is normal and expected. If you learn you have both CLL and SLL, that doesn’t mean you have a new primary cancer or that your prognosis has changed.
What do treatment options look like with CLL and SLL?
Generally, your care team won’t shift their treatment decisions based upon whether you’re navigating CLL, SLL, or both. Stage I SLL is an exception where your care team may recommend treating it with radiation therapy. Treatment decisions are based on symptoms (such as fatigue, infections, or enlarged lymph nodes), blood counts, how fast the disease is changing, and genetic features of the cancer cells.
The classification of CLL or SLL matters less. For many patients, their oncologist will monitor the disease (what’s called active surveillance) rather than immediately treat the cancer. This is because studies have shown that early treatment for these slow-growing blood cancers doesn’t necessarily improve health outcomes.
A cancer diagnosis brings with it a whole new vocabulary of terms. It’s easy to get overwhelmed. And, when your care team is moving quickly, they might forget to explain certain details of your diagnosis (like how CLL and SLL are the same yet different). Don’t ever feel badly about asking questions.
Don’t forget to join the Outcomes4Me community to connect with others who share your diagnosis.
