The MEK1E203K and N-RASG13R mutations were identified in Prog tumors derived from patients 1 and 24, respectively (Supplementary Table S2) and were also detected in our targeted screen (Table 1)....only one of the two phenotypically distinct nodules within a vemurafenib-resistant tumor (patient 24) contained mutant N-RAS. Similarly, two subclonal N-RAS mutations were identified within a single vemurafenib-resistant metastasis (42), and multiple mechanisms of resistance were detected, but did not coexist, in single-cell derived dabrafenib-resistant melanoma clone.