ERBB2 and breast cancer: The cytotoxic effect of Fmoc-FF nanogels was tested on a panel of breast cancer cells, each of which was used as a prototype of a specific breast cancer subtype: MDA-MB-361 and MDA-MB-453 (luminal breast cancer), SKBR3 (Her2 positive), and MDA-MB-231 (basal breast cancer), together with two non-tumoral cell lines, namely MCF10a (mammary gland) and 3T3-L1 (murine pre-adipocytes).