PGR and breast cancer: Similar results were obtained in MCF-7 cells, which revealed a heterozygous loss of the PR gene [16].To further analyze the OHPg/PR-B role in breast cancer cell motility, a PR negative, high motile MDA-MB-231 breast tumor cell line was transiently transfected with vector control (VC) or PR-B expression plasmids (Figure 1C).