65% patients showed a fall in Ki-67 staining with metformin; those who showed response to metformin had higher pre-treatment Ki67 levels; pAMPK, pS6, pAKT, p-4E-BP-1 and ER expression were reduced; PR unaffected; tumor proliferation decreased by 11.75% with metformin. The gene discussed is MKI67; the disease is neoplasm.