Smouldering mastocytosis: a novel subtype of systemic mastocytosis with slow progression

Systemic mastocytosis (SM) is a clonal disease that shows an either indolent or an aggressive clinical course. Utilizing established criteria, indolent SM can readily be discriminated from the rare aggressive subvariants of SM in most cases. In a small group of patients, however, clinical and laboratory parameters are indicative of slow progression without signs of aggressive disease or an associated hemopoietic neoplasm. These SM patients exhibit a high burden of mast cells, hypercellular marrow and organomegaly. Because of the 'intermediate' course and uncertain prognosis, these cases have been referred to as smouldering SM. In the present article, we discuss clinical and laboratory findings in smouldering SM and review the current literature. In addition, the pathophysiology of this novel subtype of SM is discussed.