ESR1 and leiomyoma: Real-time RT-PCR analysis of mRNA derived from isolated MMSP, MMMP, LMSP, and LMMP demonstrated that the expression levels of estrogen receptor-α (ESR1), progesterone receptor (PGR), and the smooth muscle cell markers, including αSMA, were present at very low levels in LMSP compared with both LMMP and whole leiomyoma tissues (Fig. 1C and D).