ESR1 and neoplasm: Immunohistochemically, the tumor cells were diffusely positive for vimentin (clone V9, DAKO, Glostrup, Denmark), α-smooth muscle actin (αSMA; clone 1A4, DAKO; Fig. 3a), muscle-specific actin (clone HHF-35, DAKO), and heavy caldesmon (clone h-CD, DAKO), with moderate positivity for c-kit (DAKO; Fig. 3b), estrogen receptor (ER; clone SP1, Ventana, Tucson, AZ; Fig. 3c), and progesterone receptor (PgR; clone 1E2, Ventana).