EPX and breast cancer: On the skin of Patient 3 and the breast cancer of Patient 4, specific immunostainings (anti‐eosinophil peroxidase, anti‐tryptase) and electron microscopy found numerous degranulating mast cells and eosinophils; for Patient 4, we found clustered tryptase‐expressing mast cells at the invasive front of the tumor (Figure 2B,C).