RAF1 and melanoma: It has been observed that drug-sensitive cell lines and patient biopsies typically exhibit high MITF levels, whereas inherently resistant cell lines and patient biopsies demonstrated low MITF expression but elevated levels of NF-kB signaling and the receptor tyrosine kinase AXL.454 These MITF-low/NF-kB-high melanomas display resistance to ERK, RAF, and MEK inhibition in vitro.