Limited penetration of anticancer drugs through tumor tissue: a potential cause of resistance of solid tumors to chemotherapy.

Purpose: Potential causes of drug resistance in solid tumors include genetically determined factors expressed in individual cells and those related to the solid tumor environment. Important among the latter is the requirement for drugs to penetrate into tumor tissue and to achieve a lethal concentration in all of the tumor cells. The present study was designed to characterize further the multicellular layer (MCL) method for studying drug penetration through tumor tissue and to provide information about tissue penetration for drugs used commonly in the treatment of human cancer.