Is systemic mastocytosis life-threatening?

Usually not: Most people with systemic mastocytosis (sm) have a normal lifespan. Episodes of anaphylaxis with sm can be dangerous if not treated properly, so it's important to use Epipen (epinephrine) and lay flat with the feet elevated slightly. Rarely, sm can be aggressive or associated with a leukemia. In these cases, lifespan may be shortened, but the sm may respond to chemo. See a specialist in masto for more info.