Of the four patients that progressed on BRAF inhibitor therapy (MM321, MM337, MM302 and MM358), all PDXCs demonstrated resistance to vemurafenib in HTDS (Fig. 2a), when compared with the three previously untreated BRAF-mutant melanoma lines (MM313, MM314 and MM325) (Fig. 2a). The gene discussed is BRAF; the disease is melanoma.