Frequency and prognostic impact of blood-circulating tumor mast cells in mastocytosis.

ABSTRACT Circulating tumor mast cells (CTMC) have been identified in the blood of a small number of patients with advanced systemic mastocytosis (SM). However, limited data exists about their frequency and prognostic impact in patients with mast cell activation syndromes (MCAS), cutaneous and non-advanced SM. We investigated the presence of CTMC and mast cell-committed CD34+ precursors in blood of 214 patients with MCAS, cutaneous mastocytosis and SM using highly sensitive next-generation flow cytometry. CTMC were detected at progressively lower counts in almost all advanced SM (96%) and smoldering SM (100%), nearly half (45%) indolent SM cases and few (7%) bone marrow mastocytosis patients, but were systematically absent in cutaneous mastocytosis and MCAS (P