Different clearance of KITD816V mutation and tryptase levels after haematopoietic cell transplantation in patients with systemic mastocytosis with associated haematological neoplasm.

The patterns of tryptase normalization, KITD816V clearance and establishment of donor cell chimerism were analysed in 13 patients with systemic mastocytosis and associated haematological neoplasm (AHN) after haematopoietic cell transplantation (HCT). The molecular marker of systemic mastocytosis (SM) (KITD816V) simultaneously disappeared (median + 36 days) with the establishment of donor chimerism (median: +31 days post-HCT; Pearson correlation: -0.99, p < 0.001). In contrast, tryptase normalized median of +228 days after HCT with significant delay to KITD816V clearance (p = 0.01) and full donor chimerism (p = 0.04). Faster normalization was observed after radiation-based conditioning and removal of an infiltrated spleen, while persistence was not associated with relapse of AHN.