Progesterone proves pro‐tumorigenic in both carcinogen‐induced or Brca1 loss‐driven breast cancer pre‐clinical models (Lydon et al, 1999; Gonzalez‐Suarez et al, 2010; Schramek et al, 2010; Tanos et al, 2013; Lee et al, 2016). The gene discussed is BRCA1; the disease is breast cancer.