Our single-cell RNA-seq analyses from 63 GBM patients indicate that THOC1-high cells exhibit stronger SIN3A–HDAC1/2 scaffold activity, with weaker associations for other Class I HDAC complexes such as CoREST and NuRD, supporting relative specificity for the SIN3A–HDAC1/2 axis. Here, HDAC1 is linked to glioblastoma.