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Imagine your bone marrow working overtime, making too many blood cells and throwing your body off balance. That’s what happens in myeloproliferative neoplasms (MPNs), a rare group of blood cancers. The three main types of MPNs are primary myelofibrosis (MF or PMF), essential thrombocythemia (ET), and polycythemia vera (PV) — each affecting blood cells differently.
In primary MF, abnormal blood cells grow too quickly, and scar tissue forms in the bone marrow. In ET, too many platelets are produced, and in PV, it’s too many red blood cells. Some types of leukemia, including chronic myeloid leukemia (CML), are also considered types of MPN. MPNs are considered rare because fewer than 6 people in 100,000 are diagnosed each year in the United States.
Like other cancers, MPNs are caused by genetic mutations (changes) that allow cells to divide and grow uncontrollably. There are two main types of mutations, inherited and acquired.
Inherited mutations:
Acquired mutations:
Most cancer is the result of acquired mutations. The cause of the mutation is usually unknown. MPNs are rarely associated with inherited mutations that may predispose someone to develop the disease. It’s still unclear why some people develop MPNs and others do not.
Normal cells divide in a regular, ordered fashion, forming new cells that are exact copies to replace old ones. Certain genes in each cell are responsible for telling cells when to divide and when to stop dividing. Other genes identify and fix problems in DNA that are copied incorrectly or cause cells with bad DNA to self-destruct rather than keep multiplying.
If a genetic mutation causes one or more of these genes to turn off in some cells, the cells can divide at a faster rate without regulation or order, becoming more and more mutated. Mutations can build up over time, causing abnormal cells to grow even faster. When these disordered cells begin to invade nearby tissues or break off and migrate to other locations, they become cancerous.
Although science can find links between factors and diseases, these connections don’t always mean one causes the other. Many risk factors for MPNs have been identified and are being studied to understand their role in the disease.
Because genetic mutations cause MPNs, risk factors for MPNs include anything that can encourage mutations.
Mutations in DNA happen naturally and build up as we get older. Researchers believe that in tissues that divide quickly, like blood stem cells, thousands of mutations can build up by the time you’re 60. However, cancer develops only in a small percentage of people.
The three classic types of MPNs are generally diagnosed in people over 50. PV and ET tend to be diagnosed around age 60. Although increased age is a risk factor in ET, 20 percent of cases develop in people under 40. Primary MF is most commonly diagnosed in people older than 50.
The American Cancer Society notes that the risk for CML goes up with age. Chronic neutrophilic leukemia (CNL) doesn’t have any known risk factors. The median age for CNL diagnosis is 66.5 years, and people from ages 15 to 86 have been diagnosed with the condition.
Although MPNs aren’t considered inherited diseases, it’s possible for more than one person in a family to have an MPN. In rare cases, MF and PV have been found to run in families.
According to StatPearls, PV is more prevalent among Jewish people of Eastern European descent than other Europeans and Asians.
Gender is a minor risk factor in some MPNs. According to MPN Research Foundation, women are 1.5 times more likely to develop ET than men. CML is slightly more common in men than in women.
Anything that raises the risk of acquired genetic mutations also raises the risk of MPNs and other types of cancer. Several carcinogens have been identified as contributing to the risk of MPN.
Exposure to radiation increases the risk of developing certain types of MPNs. Everyone is exposed to low levels of radiation from natural sources, such as the sky and the earth. Many building materials naturally contain low levels of radiation. Some people are exposed to naturally occurring radon gas in their homes. Human-made sources of radiation include X-rays, computerized tomography (CT) or positron emission tomography (PET) scans, and radiation therapy.
Although the levels of radiation most people are exposed to are low, the effects of radiation can accumulate over time and gradually cause mutations that sometimes lead to MPNs. People in jobs that expose them to higher levels of radiation — such as workers in nuclear power plants — may have a higher risk of CML or primary MF.
People who work with carcinogenic chemicals, such as benzene and toluene, may be more likely to develop primary MF.
Studies from the journal HemaSphere suggest that smoking a pack of cigarettes per day for 20 or more years may be a risk factor for PV in women, specifically.
Scientists have identified several acquired genetic mutations in blood stem cells that often play a role in developing MPNs. The genetic mutations usually in the three most common MPNs include the JAK2, CALR, and MPL gene markers. Mutations that disrupt the function of these genes can contribute to the uncontrolled growth of blood stem cells. Knowing which mutations are in cancer cells helps doctors recommend effective MPN treatment options.
According to the National Cancer Institute’s Dictionary of Cancer Terms:
In roughly 95 percent of people with PV, cancer cells have a JAK2 gene mutation. Specifically, the JAK2V617F gene is found in blood-forming cells.
In cases of ET, there may be mutations of JAK2, CALR, or MPL genes. About 50 percent to 60 percent of ET cases involve a JAK2 gene mutation, and roughly 5 percent involve an MPL mutation.
Between 50 percent and 60 percent of people with MF test positive for a JAK2 gene mutation. Estimates of those with MF who have the acquired genetic mutation CALR range from 3 percent to about 24 percent. In addition, 5 percent to 10 percent have a mutation of the MPL gene.
In most cases of CML, cancer cells have a genetic abnormality called the Philadelphia chromosome. This genetic change, known as BCR-ABL, was named after the city where it was discovered. It happens when part of chromosome 22 swaps places with part of chromosome 9. In rare cases of CML, there may be a different mutation in the CSF3R gene.
Mutations in the CSF3R gene are common in people with CNL.
Chronic eosinophilic leukemia has not been associated with a specific chromosome or genetic abnormality, but on rare occasions it may be linked to an acquired mutation.
MPNs are rare blood cancers caused by genetic mutations that can develop over time because of factors like aging, radiation exposure, and certain chemicals. Some mutations are inherited, but most develop during a person’s life. Knowing the risk factors, such as age, family history, and environmental exposure, can help with early diagnosis and management.
If you or a loved one has been diagnosed with an MPN, it’s important to talk with a healthcare provider to learn about treatment options based on specific genetic changes.
On myMPNteam, people share their experiences with myeloproliferative neoplasms, get advice, and find support from others who understand.
Have you or a loved one been diagnosed with MPNs? Let others know in the comments below.
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My PV was diagnosed at age 40 after a year of multiple clots and seemingly endless scans that resulted. No evidence of it in my family. Just to add to your article, it's not only red blood cells for… read more
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