How Common Is Myelofibrosis and Who Is at Risk? Explained

It is very common to ask “Why me?” after being diagnosed with myelofibrosis. In most cases, doctors cannot identify a preventable cause. Myelofibrosis (MF) is a rare blood cancer. Current research estimates the incidence (the number of newly diagnosed cases per 100,000 people in one year) to be between 0.1 and 1.8 ^[1][2]. This translates to roughly 1 to 18 new cases per million people annually.

Myelofibrosis usually affects older adults ^[3][4]. There are no proven lifestyle changes that prevent primary MF, and there is no evidence that ordinary diet, exercise, smoking, weight, or stress caused your diagnosis—you should not blame yourself ^[5]. Furthermore, myelofibrosis is not contagious. While the disease involves genetic mutations in your bone marrow cells, these are acquired during your lifetime and are generally not inherited, though an uncommon familial predisposition to blood cancers exists in a very small subset of patients ^[6][7]. Family members do not usually need screening unless recommended by a specialist.

Understanding the Incidence Rates

When researching how common myelofibrosis is, you will find different statistics depending on the source. For example, data from U.S. cancer registries estimates the incidence of primary myelofibrosis (which develops on its own) at 0.44 per 100,000 people per year ^[8]. In contrast, a recent analysis of a German health insurance database estimated the overall incidence of all myelofibrosis types to be higher, between 1.2 and 1.8 per 100,000 ^[2].

These estimates differ because of how the data is collected and how the disease is categorized:

• Registry vs. Claims Data: National cancer registries have strict diagnostic rules but can sometimes miss cases. Health insurance claims databases capture a broader population but rely on billing codes, which can sometimes be nonspecific or miscoded, leading to overestimates ^[9][2]. Both methods have limitations.
• Primary vs. Secondary Myelofibrosis: Some statistics only count primary myelofibrosis. Others combine primary cases with secondary myelofibrosis (disease that develops from a pre-existing blood condition), making the overall rate higher ^[10][11].
• Recognizing Prefibrotic Disease: The World Health Organization (WHO) recognizes prefibrotic primary myelofibrosis as a distinct diagnostic category based on specific bone marrow patterns ^[12][13]. Prefibrotic MF is not simply a guaranteed early step on the way to overt (highly scarred) MF; it is its own entity. In the past, many of these cases were diagnosed as essential thrombocythemia (ET) ^[14]. As doctors use updated criteria, more cases are classified as myelofibrosis, which shifts reported incidence rates.
• Calendar Period: As medical awareness and diagnostic tools improve, more cases are identified today that might have been missed in earlier decades ^[15].

Who is Most Likely to Develop Myelofibrosis?

While we do not know what initially triggers primary myelofibrosis, population statistics and medical research have identified several key demographics and clinical factors that describe who is most often diagnosed.

Age

Myelofibrosis is usually diagnosed in older adults, typically between 65 and 75 years of age ^[3][16]. It is much less common in younger adults, with fewer than 20% of patients diagnosed before age 50 ^[17]. While it is technically possible for children to develop myelofibrosis, pediatric cases are exceptionally uncommon and require assessment by a specialist because they behave differently than adult cases ^[18].

Prior Blood Conditions

A major recognized pathway to the disease is having a pre-existing myeloproliferative neoplasm (MPN)—a disorder involving the abnormal, clonal production of blood cells. Patients who have been previously diagnosed with polycythemia vera (PV) or essential thrombocythemia (ET) can experience an evolution of their disease into secondary myelofibrosis, known clinically as post-PV or post-ET MF ^[11][19].

The risk of this transformation varies based on individual disease features, treatments, and time. Studies following patients over time report that for PV, progression to myelofibrosis occurs in roughly 4.9% to 6% of patients at 10 years, and 6% to 14% at 15 years ^[20]. For ET, the progression risk is generally lower: about 0.8% to 4.9% at 10 years, and 4% to 11% at 15 years ^[20]. It is important to note that most people with ET or PV do not progress to myelofibrosis.

Acquired Genetic Mutations

When diagnosed, most patients are found to have acquired genetic mutations in their bone marrow cells. The most common “driver” mutations occur in the JAK2, CALR, and MPL genes ^[21]. These mutations are findings associated with the disease after it develops, not lifestyle exposures that predicted it.

Identifying these mutations helps doctors classify the disease and understand your prognosis. However, mutation status alone does not determine your risk, treatment plan, or outcome; doctors look at these alongside your blood counts, symptoms, and overall health. Furthermore, about 10% of patients lack an identifiable driver mutation in these three genes (often referred to as “triple-negative” myelofibrosis) ^[21], meaning you can still have the disease without them.