Loss of estrogen receptor ER expression is one possible cause, with between 10 and 20 of initially ER positive patients converting to negative on relapse 8 doxycycline capsule 100mg The heptapeptide decreased mitogen stimulated growth of vascular smooth muscle cells VSMC in vitro 11 and attenuated neointima formation in a balloon catheter injury model of the rat carotid artery, with no effect on the underlying media layer, indicating that the antigrowth properties of the heptapeptide are limited to proliferating cells 12