ESR1 and leiomyoma: Immunostaining was negative for S100, Ki67, STAT6, and CD34 (Figure 4), confirming no malignancy, and positive for estrogen receptors (ER40), desmin, h-caldesmon, and α-smooth muscle actin (αSMA) (Figure 4), diagnosing an estrogen receptor-expressing leiomyoma of muscle origin.