Chronic Myeloid Leukemia Facts

April 19, 2024 
This page was reviewed under our medical and editorial policy by Guido Marcucci, M.D., Chair, Department of Hematologic Malignancies Translational Science, City of Hope Duarte

Chronic myeloid leukemia is a rare blood cancer that mainly affects adults. This blood disorder is sometimes called CML leukemia, chronic myelogenous leukemia or CML. It accounts for about 0.5% of all new cancer diagnoses in the United States each year, according to the National Cancer Institute (NCI).

In terms of numbers of patients, data from NCI show the number of people in the U.S. living with CML at the start of 2020 was:

• 30,765 among those aged 65 and over (0.1%)
• 27,966 among those aged 40 to 64 (less than 0.1%)
• 7,636 among those under age 40 (less than 0.1%)

Leukemia is a broad blood cancer category. About 15% of people diagnosed with a new case of leukemia have chronic myeloid leukemia, and one in 526 people develop the cancer in their lifetimes. The number of CML cases is fairly equal among men and women, although men are slightly more likely to be diagnosed than women.

What Is Chronic Myeloid Leukemia?

CML is a type of slow-growing blood cancer that starts in the bone marrow, where cells known as myeloid stem cells are made. Normally, many of these myeloid stem cells form into mature white blood cells called granulocytes. Healthy granulocytes help the immune system fight infections and disease.

CML occurs when myeloid stem cells change or mutate, resulting in an overproduction of abnormal, unhealthy granulocytes. These abnormal cells grow out of control, leaving less room in the bloodstream for healthy white blood cells, red blood cells and platelets (clotting agents). For patients with CML, this may lead to increased infections and anemia, as well as excessive bleeding and bruising.

What Causes Chronic Myeloid Leukemia?

A type of mutation called an acquired mutation is the cause of CML. An acquired mutation is an injury to the DNA (genetic material) that happens after a person is born. Although outside factors such as exposure to environmental chemicals or radiation may lead to acquired mutations, often the damage occurs without any known reason.

For most people diagnosed with CML, DNA injury triggers genetic material to break off from one chromosome and reattach to another. The newly formed chromosome is called the Philadelphia chromosome, and it’s made up of a gene that causes myeloid stem cells to produce an abnormal protein. This abnormal protein triggers overproduction of abnormal white blood cells, called granulocytes or blasts.

Is Chronic Myeloid Leukemia Hereditary?

Chronic myeloid leukemia is not hereditary. In hereditary gene mutations, the mutation is contained in the original cells that form when a sperm cell fertilizes an egg, passing from parent to child. This is not the case with CML. Instead, the gene mutation that causes CML cancer starts in the bone marrow cells of the person who acquired the mutation after birth.

This means people won’t inherit the mutation that causes CML from their parents. It also means that they will not pass the CML gene mutation on to their children.

CML Risk Factors

Although there’s no clear-cut reason why a person develops CML, certain risk factors are associated with the condition. A risk factor is anything that may increase a person’s chances of being diagnosed with a disease such as cancer.

The three known risk factors for developing chronic myeloid leukemia are listed below.

Gender: Men are diagnosed with CML at a slightly higher rate than women.

Age: People over age 40 are diagnosed with CML at significantly higher rates than younger people. The average age at diagnosis is 64.

Radiation exposure: People exposed to high-dose radiation due to a nuclear reactor accident or atomic bomb explosion are more likely to develop CML than the general population. Most people who have radiation therapy, X-rays or computed tomography (CT) scans as part of their medical care are not at increased risk of CML. A slightly higher risk is associated with high-dose radiation therapy for other cancers, although most people undergoing this treatment don’t develop CML.

City of Hope^® offers state-of-the-art diagnostic tests and treatments for CML, along with an expert team of cancer doctors whose mission is to provide excellence in treatment and support for patients and their family members.