The progesterone derivative fluoro furanyl norprogesterone (FFNP), radiolabeled with fluorine F 18, with positron-emitting radioligand activity. Upon injection, fluorine F 18 fluoro furanyl norprogesterone (F18-FFNP) binds to progesterone receptors (PgR) in progesterone-responsive tissues. In PgR-positive breast cancer, positron emission tomography (PET) may then be used to quantitate hormone receptor status. Check foractive clinical trials using this agent.