Why does myelofibrosis cause anemia?

Bone marrow is the tissue found at the center of bones. While the exterior of bone is hard and solid, bone marrow is soft and spongy, and contains a dense network of blood vessels. Most of the body’s blood cells are made in bone marrow.

Myelofibrosis (MF) is a type of cancer that causes scarring (fibrosis) in the bone marrow. It is categorized as a myeloproliferative neoplasm, a type of cancer where the bone marrow produces excess amounts of abnormal blood cells.

MF can be categorized as primary and secondary, depending on the cause. Primary MF occurs on its own, and the underlying causes are not fully understood. Secondary MF evolves from another disorder, usually another type of blood or bone marrow cancer. Secondary MF is less common than primary MF, accounting for 10 to 20 percent of cases.

One of the main features of MF is anemia.

What is anemia?

Anemia occurs when the body does not have enough healthy red blood cells and/or does not have enough hemoglobin:

• Red blood cells transport oxygen from the lungs to cells throughout the body. They also transport carbon dioxide (produced when cells use oxygen) to the lungs so that it can be exhaled from the body.
• Hemoglobin is a protein found in red blood cells. Hemoglobin is what oxygen attaches to so it can be transported throughout the body. Hemoglobin is also what carbon dioxide attaches to so it can be carried to the lungs and exhaled.

All cells in the body rely on a steady, continuous supply of oxygen in order to function and remain alive. When that supply of oxygen is reduced, it causes problems. Fatigue, weakness, shortness of breath, and pale skin are common symptoms of anemia caused by MF.

How does MF cause anemia?

MF contributes to anemia in several ways:

• As described above, MF causes an overproduction of diseased blood cells. These diseased cells take up space inside the bone marrow, displacing healthy blood cells before they can mature.
• Another feature of MF is an enlarged spleen, an organ that (among other functions) filters out damaged red blood cells. An enlarged spleen can become overactive, removing healthy red blood cells from circulation.
• MF is also associated with an increased volume of plasma (the liquid part of blood). This does not reduce the number of red blood cells, but it does dilute the concentration of red blood cells.
• Described above, MF causes scarring in the bone marrow. Since scar tissue cannot produce blood cells, there is less bone marrow available to produce red blood cells.
• Inflammation that results from MF also disrupts the body’s ability to effectively use iron, a mineral that is one of the main components of hemoglobin.
• MF also impacts the production of platelets, blood cell fragments that circulate in the blood and prevent and stop bleeding. With low numbers of platelets, a person may bleed and bruise easily, further reducing the amount of red blood cells.

What are the treatments for anemia?

Treating and or/preventing anemia are important to the treatment of MF. Blood transfusions and medications to improve red blood cell counts are often a part of treatment.

Anemia is also a consideration when choosing therapies to treat MF, as some therapies can worsen anemia. Several new and emerging therapies being used in the treatment of MF have been shown to improve anemia.