NOTCH4 and ductal breast carcinoma in situ: An EGFR tyrosine kinase inhibitor (gefitinib), a γ-secretase inhibitor (DAPT), a goat anti-human Notch-4-neutralizing polyclonal antibody (clone-N17 without sodium azide), and a goat immunoglobulin G were added to DCIS cells suspension at time of plating and the mammospheres were counted on day 3 after plating.