PGR and breast cancer: We observed that the EC50s for HMA-mediated tumorsphere suppression toward bulk populations of MDA-MB-231 (ER/PR/HER2-), MCF7 and T47D (ER/PR+), and SKBR3 (HER2+) human breast cancer cell lines (see Table S1) are essentially identical to each other (Figure 1A) and identical to the EC50s we previously reported for HMA cytotoxicity toward the total populations of these cell lines [17].