ERBB2 and neoplasm: Indeed, in ER/PR-negative Her2-dependent mouse primary tumor cells, the addition of progesterone to charcoal-stripped serum, which is depleted of lipid-soluble hormones such as progesterone, did not affect the ability of Paqr8 overexpression to enhance, or Paqr8 deletion to impair, cell viability following Her2 downregulation.