HDAC1 and neoplasm: As shown above, Eμ-myc tumor development was significantly delayed in mice having a single allele of Hdac2 and no Hdac1 (Hdac1Δ/Δ; Hdac2Δ/+), while this was not the case in mice with a single allele of Hdac1 and no Hdac2 (Hdac1Δ/+; Hdac2Δ/Δ; Fig. 2).