Until recently, treatment of certain rare and serious blood disorders, known as myeloproliferative diseases, addressed symptoms rather than the disease itself. This group of disorders, which are kinds of cancers, occur when the body makes too many or not enough of one or more of the types of blood cells: red, white and platelets. Three of the main rare blood disorders are polycythemia vera (PV), myelofibrosis (MF) and essential thrombocythemia (ET). They can be serious and potentially life-threatening and, in a small number of cases, lead to another form of fast moving cancer called acute myelogenous leukemia, or AML. In the past few years, however, researchers have developed a new treatment that is changing the outlook for many people with myeloproliferative diseases, offering hope for longer lives as well as relief from symptoms. There are other new drugs in the pipeline for rare blood disorders too, some of which are in the final stages of clinical testing. The Breakthrough Before 2005, doctors didn’t know what caused PV, MF and ET, but that year, two teams of researchers independently discovered that a mutation in the JAK2 gene was behind the diseases. The JAK2 gene produces an enzyme that is inside all cells and signals the body to make blood cells. In patients with the mutation, the JAK2 enzyme is produced even when the body isn’t sending the signal, causing abnormal cell growth. Armed with the knowledge of what was behind the rare blood disorders, researchers could pursue new ways to treat them. They began working with drugs called JAK2 inhibitors, which they hoped would stop the mutations from sending the wrong signals. The Advances In 2011, the FDA approved the use of the first JAK2 inhibitor, ruxolitinib (Jakafi), to treat some types of myelofibrosis, the most aggressive of the three disorders. In 2014, it became the first drug approved for a second rare blood disorder, polycythemia vera. Ruxolitinib was effective in controlling abnormal blood counts and reducing the size of enlarged spleens, lessening symptoms and improving quality of life. Ruxolitnib is generally prescribed for people for whom hydroxyurea, an earlier treatment, did not work or made them feel too sick to take it. Ruxolitnib was a major leap forward in treating rare blood disorders, and now there are new types of JAK2 inhibitors under study, as well as other avenues of promising research for myeloproliferative diseases. A drug called Everolimus, which is FDA approved to treat some other types of cancer, reduced spleen size and some symptoms during clinical trials in people with MF. A medication called pomalidomide has done well in clinical trials, effectively treating anemia, which is a major problem in people with rare blood disorders. It works by telling the body’s immune system to attack abnormal cells, in order to make room for normal cells that can then produce healthy red blood cells. Researchers also continue to investigate a class of drugs called epigenetics, a broad term that covers drugs that affect unwanted changes in the way genes behave as they turn on and off. Epigenetic changes are linked to many diseases, including various cancers. All these new areas of research, from JAK2 inhibitors to epigenetics, hold promise, but traditional treatments still have their place. Established Treatments Phlebotomy, a technique in which healthcare professionals take some of your blood to reduce excess red blood cells, has been around for centuries. They are an effective tool used to remove excess and unhealthy blood cells. Today, a phlebotomy is a simple procedure, similar to donating blood. You may also be prescribed the drug called hydroxyurea, which can lower elevated blood cell counts, but not all patients can tolerate it. Another option is interferon, which may stimulate the immune system to slow the overproduction of red blood cells. If you have PV or ET, your doctor may tell you to take low-dose aspirin to reduce the risk of clotting. If you have MF, you may be a candidate for a bone marrow transplant, which can potentially cure the disease, but only a small number of patients can have this risky procedure, which may be fatal. There are also symptomatic treatments and medications that your doctor can give you that can reduce pain, fatigue, itching and inflammation that may come with any of the three conditions. These older but often effective treatments, along with the new frontiers in treating rare blood disorders, offer people living with them new avenues for managing their conditions and living longer, healthier lives. For the estimated 300,000 people living with rare blood disorders in the United States, the recent advances are a welcome step forward.