RON activation in cancer can occur through MSP-mediated stimulation of the receptor and/or by overexpression of the receptor independent of its ligand.4,17 In order to examine both ligand-dependent and ligand-independent RON activation, we engineered human estrogen receptor positive breast cancer cells (T47D cells) to conditionally overexpress RON upon addition of doxycycline. The gene discussed is ESR1; the disease is breast carcinoma.