A critical reappraisal of treatment response criteria in systemic mastocytosis and a proposal for revisions

Mast cell disease (MCD) is a hematopoietic stem cell neoplasm that is associated with infiltration of one or more organs with cytologically abnormal mast cells (MC). MCD is frequently but not always associated with a KIT mutation and, in some cases, is associated with clonal expansion of non-MC lineage cells. In adults, there is almost always MC infiltration of the bone marrow, which is a cardinal feature of systemic mastocytosis (SM). While, as members of the wider community of physician scientists, we recognize the contribution of the current consensus treatment response criteria for SM, as individuals with more than average clinical experience in SM, we would like to point out their limitations and engage in a constructive discussion that will hopefully lead to a consideration for revisions. We present here an alternative proposal for treatment response assessments we believe is more objective, reproducible, and importantly, SM-subtype specific, given the recent progress in our understanding of the natural history of this disease. We believe this proposal is timely given the prospects for new clinical trials in SM, and the related regulatory aspects of new drug approval that are currently not adequately addressed. The intent of this exercise is not to undermine the complexity of the disease or previous work by other investigators, but to come up with ideas for response criteria that are more practical and consider meaningful patient outcome.