Particular cell markers, signaling pathways, cell surface receptors, such as folate, transferrin and epidermal growth factor receptor (EGFR), as well as stem cells, immune cells, stromal cells, and fibroblasts, may be used for targeting as they are either upregulated, downregulated or mutated in rapidly dividing cells during cancer [18,81,103,104,105,106]. Here, EGFR is linked to cancer.