Mastocytoma – Wikipedia

A mastocytoma or mast cell tumor is a type of round-cell tumor consisting of mast cells.It is found in humans and many animal species; it also can refer to an accumulation or nodule of mast cells that resembles a tumor.. Mast cells originate from the bone marrow and are normally found throughout the connective tissue of the body as normal components of the immune system.

https://en.wikipedia.org/wiki/Mast_cell_tumor