We first noticed that citarinostat was significantly more cytotoxic to the parental human KB-3-1 epidermal cancer cells and the parental human S1 colon cancer cells than to the respective ABCB1-overexpressing variant KB-V-1 (R.F = 15, Figure 1A) and ABCG2-overexpressing variant S1-M1-80 (R.F = 21, Figure 1B) cells. The gene discussed is ABCG2; the disease is malignant colon neoplasm.