Origin of stem cells in the BM niche: new clues from mastocytosis.

In this issue of Blood, Garcia-Montero et al reported that in nearly 30% of patients with indolent systemic mastocytosis (SM), the characteristic c-kit mutation D816V, is not restricted to mast cells, but may also be found in bone marrow (BM)–derived mesenchymal stem cells (MSCs), also known as BM stromal cells (BMSCs). Thus, the notion that mastocytosis is a disease driven exclusively by mutations in blood cells, especially mast cells, has now been challenged.