Our hypothesis that serum GGT might be associated with response to docetaxel was generated based on interesting preclinical findings that GGT-positive PC3 cells were more resistant to the toxicity of cisplatin than GGT-negative PC3 cells, since the former could cleave extracellular GSH and thus provided additional cysteine required for diminishing the tumor toxicity of cisplatin [21]. This evidence concerns the gene GGT1 and neoplasm.