During treatment with vemurafenib 960 mg b.i.d. + PEG-IFN-α-2b 1 μg/kg once weekly, dose-limiting toxicity (DLT) neutropenia grade (G)4 and leukopenia G4 related to the study drugs (vemurafenib plus PEG-IFN) has been observed. Here, IFNA1 is linked to neutropenia.