Staging chronic myeloid leukemia

Staging is a way of describing or classifying a cancer based on the extent, or amount, of cancer in the body. Cancers that form solid tumours are given numbered stages based on the size of the tumour and if the cancer has spread to lymph nodes or other parts of the body.

Chronic myeloid leukemia (CML) is not staged in the same way as other types of cancer. Because it is a cancer of the cells in the blood-forming tissue in the bone marrow, it doesn't form a solid tumour. Instead of a stage, CML is given a phase.

Each phase of CML is based on the number of blast cells (immature blood cells) in the blood and bone marrow. Several different systems are used to describe the phases of CML, but the MD Anderson (MDA) criteria is used most often in Canada. Your healthcare team uses the phases of CML to help determine your prognosis and what treatments to offer you.

CML develops very slowly. With treatment, it can stay in the chronic phase for many years. If CML starts to progress, it usually passes through each of the phases described below. Sometimes it can progress from the chronic phase directly to the blast phase. When CML moves into the blast phase from either the chronic or accelerated phase, it may be called a blast crisis.

In the chronic phase of CML, less than 10% of the cells in the blood and bone marrow are blast cells. Most people are diagnosed with CML in the chronic phase.

You may have mild symptoms, such as being tired and losing a little weight. Some people have no symptoms at all. As a result, CML in the chronic phase is often found during routine blood tests done for other reasons.

During the accelerated phase of CML, the abnormal granulocytes with the BCR-ABL gene (called leukemia cells or CML cells) continue to build up. Other genetic changes also occur. These changes make the blast cells reproduce more quickly. As a result, the number of blast cells in the bone marrow increases and they start to appear in large numbers in the blood.

In the accelerated phase of CML, between 10% and 19% of the cells in the blood and bone marrow are blast cells. These blast cells crowd out the healthy red blood cells, white blood cells and platelets. The changes in the numbers of blood cells cause more symptoms. You may start to feel more tired and lose more weight. You may also have swelling and pain in your abdomen if your spleen is getting larger.

CML in the accelerated phase doesn't respond to treatment as well as it does in the chronic phase. It can quickly progress to the blast phase.

CML in the blast phase has become rare because of how well it can be treated with targeted therapy. If CML does progress to the blast phase, it starts to act differently. The blast cells build up in the blood and bone marrow more quickly.

In the blast phase of CML, 20% or more of the cells in the blood and bone marrow are blast cells.

When CML is in the blast phase, you may have a fever, poor appetite, weight loss, fatigue and malaise, shortness of breath and pain in your abdomen or bones.

CML in the blast phase may change into a different type of acute leukemia. Most often, it changes into acute myeloid leukemia (AML). In rare cases, it may change into acute lymphoblastic leukemia (ALL).

Refractory CML means that the number of granulocytes with the BCR-ABL gene (called leukemia cells or CML cells) has increased after treatment.

There are 2 types of refractory CML.

• Primary refractory disease means that CML hasn't responded to any treatment.
• Secondary refractory disease means that CML has stopped responding to treatment.