Human breast cancer cell lines, MCF-7 and ZR-75-1 (ER+/PR+/HER2/neu−), and the triple-negative MDA- MB-231 cell line (ER−/PR−/HER2/neu−) were grown as spheres on agarose-coated flasks in an enriched medium for stem-like cells, as described for the small cell lung cancer (SCLC) cell line H446 [28] and bronchial carcinoid cell lines (H727 and H720) [23]. Here, ERBB2 is linked to breast cancer.