IDH1 and pilomyxoid astrocytoma: IDH1 mutations, NTRK2, MYB, and MYBL1 rearrangements, and ATRX loss: Among patients with pilocytic or pilomyxoid astrocytomas who had testing for IDH1 mutations (n = 15), rearrangements of NTRK2 (n = 9), MYB (n = 10), or MYBL1 (n = 7), and ATRX loss (n = 10) performed on both paired surgical specimens, results remained negative in all paired samples, with no acquisitions or losses, including after systemic therapy or irradiation (Table 2).