Polycythemia vera (PV) is a rare blood cancer, but it’s one of the more common diseases within the rare disease category. In children and young adults, the incidence drops to roughly 0.18 per 100,000 per year, making it exceptionally uncommon before middle age. Most people diagnosed are in their 60s or older, and men are affected slightly more often than women.
How Common Is PV by the Numbers?
PV belongs to a group of blood cancers called myeloproliferative neoplasms. Among adults, it’s the most frequently diagnosed disease in this group, yet it still qualifies as rare by any standard medical definition. In children and young adults, the incidence is estimated at just 0.18 per 100,000 people per year. For context, that means fewer than 2 children or teens per million develop PV in any given year.
The disease becomes significantly more common with age. The median age at diagnosis is 67, and the vast majority of patients are diagnosed after age 50. In a large U.S. observational study of 2,510 patients (the REVEAL study), 54.2% were male and 89.1% were white, suggesting a demographic skew toward older white men, though PV occurs across all ethnic groups.
Why It Develops
Nearly all cases of PV trace back to a single genetic glitch. About 95% of patients carry a mutation called JAK2 V617F, which causes bone marrow to overproduce red blood cells. The remaining patients who don’t have that specific mutation almost always carry a related mutation in a different section of the same gene (JAK2 exon 12). This means PV is one of the few cancers where a single genetic test can confirm the diagnosis in the vast majority of cases.
The JAK2 mutation is acquired during a person’s lifetime rather than inherited. You don’t pass it to your children the way you would a hereditary condition. Why certain people develop the mutation and others don’t remains unclear, though advancing age is the strongest known risk factor.
How PV Is Diagnosed
Diagnosis typically starts with a blood test showing unusually high red blood cell levels. Current guidelines set the threshold at a hemoglobin level above 16.5 g/dL (or hematocrit above 49%) in men and above 16.0 g/dL (or hematocrit above 48%) in women. If your blood counts are elevated, your doctor will usually order a test for the JAK2 mutation.
Most patients also undergo a bone marrow biopsy to confirm the diagnosis. Under a microscope, PV bone marrow looks distinctly overcrowded, with an overproduction of red blood cells, white blood cells, and platelets all at once. This pattern, called panmyelosis, helps distinguish PV from other conditions that can raise red blood cell counts, like chronic dehydration or sleep apnea.
Thrombosis: The Main Danger
The thick, slow-moving blood that results from excess red blood cells creates a real risk of blood clots. In a study of 587 PV patients at a single center, 25% had experienced a blood clot either before or at the time they were diagnosed. Of those who had already clotted once, 27% went on to have a second clotting event after their PV diagnosis. These clots can show up as strokes, heart attacks, deep vein thrombosis, or clots in unusual locations like the veins draining the liver or spleen.
This is why treatment focuses heavily on keeping blood thickness under control, typically through regular blood draws (phlebotomy) and low-dose aspirin. For higher-risk patients, medications that reduce blood cell production may be added.
Long-Term Survival and Progression
PV is a chronic condition, not an immediately life-threatening one, but it does shorten life expectancy compared to the general population. In an international study of 1,545 patients, the projected median survival for the full group was 18.9 years from diagnosis. A subset with the most complete follow-up data showed a median survival of 14.1 years, significantly worse than age-matched peers without PV.
Risk varies considerably by individual. The same study developed a prognostic model that separated patients into three groups: low-risk patients had a median survival of 26 years, intermediate-risk patients about 15 years, and high-risk patients roughly 8.3 years. Factors that push patients into higher risk categories include older age at diagnosis, history of blood clots, and elevated white blood cell counts.
Over time, PV can transform into more aggressive diseases. The accumulated risk of transformation to acute myeloid leukemia is estimated at 2.3% to 14.4% over 10 years, a wide range that reflects differences in patient populations and treatments studied. PV can also progress to a scarring condition of the bone marrow called myelofibrosis, which impairs the marrow’s ability to produce blood cells normally. Both transformations are serious, but many patients live for decades without experiencing either one.
PV in Children and Young Adults
Pediatric PV is genuinely rare. A French study collecting cases from seven pediatric cancer centers over many years identified only 2 PV patients under age 18 across all those centers combined, compared to 15 with the related condition essential thrombocythemia. The global incidence in children and young adults is estimated at 0.18 per 100,000 per year.
When PV does occur in younger patients, the biology can look different. Children with PV are less likely to carry the JAK2 mutation that defines nearly all adult cases, which can make diagnosis more challenging. The clinical course also tends to differ, with some younger patients having a more indolent disease and others presenting unique complications that require specialized pediatric hematology expertise.