ACVR1 and astrocytoma (excluding glioblastoma): mHGAs (Midline High-Grade Astrocytomas) are another type of pediatric cancer caused by a H3.3K27M substitution mutation in the downstream signaling receptor, ACVR1 (Activin A Receptor Type 1), which causes subsequent hyperactivation of BMP (Bone Morphogenetic Protein)–ACVR1 developmental signaling pathways, and ultimately upregulates downstream early-response genes in tumor cells (Figure 1) [92].