IDH2 and cholangiocarcinoma: Mutations of IDH1 and IDH2 have been identified in over 70% of lower-grade gliomas (LGGs; World Health Organization (WHO) grade II/III) and secondary glioblastoma (GBM) [1,2], and at lower frequencies in a variety of other human malignancies, including acute myeloid leukemia (AML; ≈30%), chondrosarcoma (≈50%), cholangiocarcinoma (≈15–20%), thyroid carcinoma, melanoma, angioimmunoblastic T-cell lymphoma, and in a rare subtype of breast cancer [3,4,5,6,7,8].