EGF and neoplasm: Surrogates were connected to a micro-peristaltic pump and a media reservoir via peroxide cured silicone tubing (Cole Parmer), as previously described41, and continuously perfused with 15 mL medium (HMMEC media containing 5% FBS and antibiotics for cell line surrogates or mammary epithelial media for murine tumor surrogates (Phenol Red Free DMEM/F12 supplemented with 10% FBS, 20 ng/ml EGF, 0.5 μg/ml hydrocortisone, 100 ng/ml cholera toxin, 100 μg/ml bovine insulin, and antibiotics) for 1 to 14 days (37 degrees, 5% CO2), with medium changed every 3 days.