Troche has saved the lives of many lung cancer patients, but it has also made many patients suffer from severe rash, why does the rash appear? Let me explain to you. Troche is called epidermal growth factor receptor inhibitors (EGFRIs). Epidermal growth factor (EGF) was discovered by Cohen and Montalcini in the 1950s while studying murine nerve growth factor, and is similar to epidermal growth factor receptor (EGFR). epidermal growth factor receptor (EGFR) activates EGFR’s own tyrosine kinase upon binding, thus playing an important role in cell proliferation, differentiation regulation, and tumor transformation []. This locus has become an important target for tumor therapy. Antitumor drugs that target EGFR include monoclonal antibodies and small molecule tyrosine protein kinase inhibitors, collectively known as epidermal growth factor receptor inhibitors. (EGFRIs). Among them, epidermal growth factor receptor inhibitors have outstanding effects, such as gefitinib and erlotinib for lung cancer, sunitinib for kidney cancer, and gleevec for chronic granulocytic leukemia and gastrointestinal mesenchymal tumor. (gleevec) and cetuximab for chronic granulocytic leukemia and gastrointestinal mesenchymal tumors. It plays an important role in the proliferation and differentiation of epidermal cells: stimulating their growth, inhibiting their differentiation, protecting them against UV-related damage, inhibiting inflammation and accelerating wound healing. In normal skin tissues, phosphorylated epidermal growth factor receptors are highly expressed in the basal and suprabasal layers, and in the outer hair root sheath, which are areas where proliferating and undifferentiated keratin-forming cells are more abundantly distributed. In other words, not only tumor cells have epidermal growth factor on their surface, but also this receptor is present in normal skin. When using Troche, tumor cells don’t grow anymore, and neither do normal skin cells! The other normal functions of the skin are also gone! Therefore, it is currently believed that keratin-forming cells of the skin are the main targets mediating the occurrence of cutaneous adverse reactions to EGFRIs. EGFRIs, by competitively inhibiting the binding of ATP to the cytoplasmic region of the receptor, thereby preventing phosphorylation and kinase activation, can affect the proliferation, differentiation, migration, and adhesion of keratinized cells, leading to the formation of papular pustules and the development of desiccation.