In mouse thymic lymphoma, HDAC1 deletion results in oncogenic transformation (Vlaming et al., 2019), whereas in the case of CTCL reduced HDAC activity has tumor-suppressing consequences (Lopez et al., 2018; Chen et al., 2020; Pavlidis et al., 2021). The gene discussed is HDAC1; the disease is primary cutaneous T-cell non-Hodgkin lymphoma.