KIT and small cell lung carcinoma: Other well-known cellular pathways related to carcinogenesis are represented by receptor tyrosine kinase (RTK) and in SCLC are found alterations in IGF-1R (insulin-like growth factor receptor 1), FGFR1 (fibroblast growth factor receptor 1), KIT, MET (mesenchymal epithelial transition) and EGFR [69,70,72].