A plain language summary of the BASIS study looking at people living with severe hemophilia A or B with inhibitors and being treated with marstacimab

Summary What is this summary about? This summary describes a clinical study looking at how well marstacimab works in people living with hemophilia with inhibitors. The study was published in the medical journal Blood . Hemophilia is caused by not having enough blood clotting factors, which are proteins found in the blood that help form a clot and stop bleeding. People living with hemophilia either don’t make these proteins, have low amounts of these proteins, or these proteins do not work well. Hemophilia is usually inherited from biological parents, meaning it is passed on to their children through genes. In some cases, hemophilia happens even if no one in the family has it. There are some treatments to replace the missing clotting factor. This type of treatment is called factor replacement therapy and contains the missing clotting factor proteins. Some people make antibodies against the replacement clotting factors, so the replacement clotting factors do not work as well as they need to for the blood to clot. This is called hemophilia with inhibitors. People who have hemophilia with inhibitors need to take medicines called bypassing agents instead of replacement clotting factors. These medicines aim to activate the body’s blood clotting system, but do not always work well. They also need to be injected into a vein, known as intravenous infusion, or IV infusion for short. IV infusions are taken several times a week. Different options to IV factor replacement therapy for people living with hemophilia A or hemophilia B are called non-factor replacement therapy. A protein in the blood called Tissue Factor Pathway Inhibitor, or TFPI, can also prevent blood clotting. Marstacimab is a type of non-factor replacement therapy that attaches to TFPI and stops its activity. For people living with hemophilia, marstacimab can help blood to form a clot when needed. Marstacimab is injected under the skin. This can be an easier way to receive medicine than an injection into a vein. Marstacimab offers a new way to treat people living with hemophilia. What were the results of the study? The study showed that people living with hemophilia with inhibitors who were treated with marstacimab had fewer bleeding events over 1 year compared to previous therapy with bypassing agents. Most side effects with marstacimab treatment were minor or could be easily managed. One person stopped taking marstacimab treatment because they developed a skin rash that got better over time. What do the results mean? The study showed that marstacimab could help prevent bleeding in people living with hemophilia A or B with inhibitors.