Since EGFR is critically involved in activating the intracellular downstream signaling cascades, such as PI-3 kinase and MAPK signaling pathways, leading to proliferation and survival of breast cancer cells [66,87,88,89,90], treatment of MCF-7 and 4T1 cells with EGFR targeting anti-siRNA-loaded PEG-SSNs and SSNs for a consecutive period of 48 h was found to significantly kill the cancer cells (Figure 9). Here, EGFR is linked to breast cancer.