First, near the entrance of the pocket, the cyclohexylamine of UM171 and the X1 position of the two cancer mutants (that is, Pro311 of KBTBD4-PR and Thr311 of KBTBD4-TTYML) both contact the same HDAC1 loop comprising Asp99 and Glu98 (Fig. 4d,e, and site 1 Fig. 4a). Here, KBTBD4 is linked to cancer.