NF1 and colonic neoplasm: For example, a cell-line study identified loss-of-function mutations in NF1 (a negative regulator of RAS activity) in tumors that were intrinsically resistant to treatment with BRAFi.12 In our study, one patient with colon cancer had a comutation in NF1: this patient had disease control on BRAF-targeted therapy for 16 weeks before progression.