The MFB tumor cells show immunoreactivity for CD34, desmin, and, variably, with smooth muscle actin (SMA), estrogen receptor (ER)/progesterone/androgen receptor, CD99, B-cell lymphoma 2 (Bcl2), and CD10 [8,21,28], and they do not express cytokeratins or p63. The gene discussed is ESR1; the disease is neoplasm.