As the acetylated androstano-arylpyrimidines could sensitize multidrug-resistant cancer cells to undergo apoptosis induced by certain chemotherapy agents, we hypothesized that semi-synthetic acetylated dihydrotestosterone derivatives might modulate the efflux function of Colo 320 cancer cells by suppressing the expression of the inherently present and overexpressed ABC transporters that are generally accountable for the drug resistance in MDR cancer cells. This evidence concerns the gene ABCG2 and cancer.