Successful treatment of systemic mastocytosis with high-dose interferon-alfa: long-term follow-up of a case.

Daily treatment of systemic mastocytosis with high-dose interferon-alfa often is not tolerated because of clinical or hematologic side effects. We report successful treatment of a patient with systemic mastocytosis, who was positive for the D816V mutation, with interferon alfa-2b at 10 million units three times per week. During 5 years of treatment, bone marrow infiltration by mast cells decreased from 50 to < or =5%, and there was a decrease (urinary N-methylhistamine excretion, 75%; serum tryptase concentration, 98%) or normalization (serum calcitonin value, urinary prostaglandin F2alpha excretion) of mast cell mediators. Side effects included mild depression (untreated) and biochemical hypothyroidism easily managed with supplemental levothyroxine.