EGFR and skin cancer: Furthermore, in vitro studies were performed using a medium-level EGFR-expressing skin cancer cell (A431, EGFRmedium) and low-level EGFR-expressing lung cancer cell (A549, EGFRlow) to evaluate anti-tumor and cellular uptake efficiency via MTT assay and single-particle inductively coupled plasma mass spectrometry (spICP-MS), respectively.