For NF1 patients, a biopsy is generally not indicated, even for the detection of BRAF mutation status, before initiating treatment with a MEK 1/2 inhibitor (e.g., selumetinib) for recurrent or progressive tumor growth, and is reserved for cases with suspected tumor transformation or an unusual location and/or presentation [34, 45]. The gene discussed is MAP2K1; the disease is neoplasm.