ACVR1 and central nervous system cancer: Surprisingly, mice that were infected with ACVR1 R206H, Cre, and PDGFA but not H3.1K27M or ACVR1 R206H, H3.1 WT, Cre, and PDGFA did not demonstrate an increase in tumor incidence (21/26 = 81% and 11/25 = 44%, respectively) compared to any group except each other (Fig. 4d and Table 2), suggesting that H3.1K27M is required for the effect of ACVR1 R206H on tumor initiation and is in agreement with our observations with the glioma-like lesions without PDGFA.