KIT and CPA3 are canonical markers of mast cells. KIT (CD117) is a receptor tyrosine kinase essential for mast cell development, survival, and activation, and is highly expressed on mast cells. CPA3 (carboxypeptidase A3) is a mast cell–specific granule protease reflecting their secretory and effector function. KIT and CPA3 reliably identify mast cells and distinguish them from other immune cell populations.