Cell spheroids: the new frontiers in in vitro models for cancer drug validation.

During the past decades, evaluation of anticancer drugs utilizing 2D cell cultures has been in common usage. In contrast to 2D cell cultures however, which lack many characteristics of the complex in vivo situation, 3D cell or tissue culture systems, such as cellular spheroids, better mimic the crucial tumor tissue properties and the microenvironment, and are thus more appropriate for the evaluation of pharmaceutical candidates. Taking the characteristics of the tumor microenvironment into consideration, crucial aspects and recent advances related to cell spheroids in the validation of anticancer drugs are discussed here.