ABCG2 and cancer: ABC transporters are membrane-bound transport proteins that are ubiquitously present in the human body.1-4 They play a major role in determining the distribution of intrinsic and xenobiotic drugs between intra- and intercellular compartments.5,6 The clinical relevance of ABC transporters became pronounced when their expression was correlated to cross-resistance of cancer cells to antineoplastic agents.3,7-13 This phenomenon is called ‘multidrug resistance’ (MDR).