Indolent systemic mastocytosis and aleukemic mast cell leukemia: Subtle diagnostic differences with distinct management approaches.

Mastocystosis is characterized by accumulation of mast cells in tissues, with systemic disease presenting on a spectrum of severity. Indolent systemic mastocytosis (ISM) is marked by absence of hepatosplenomegaly, bone marrow, skeletal, or gastrointestinal (GI) dysfunction. Smoldering systemic mastocytosis (SSM) presents with involvement of the bone marrow, liver, spleen, and lymph nodes.1 Both indolent and smoldering subtypes have a better prognoses than advanced systemic mastocytosis, including mast cell leukemia (MCL).