The potential for immunotherapy as a treatment option for cancer is clear from remarkable responses of some leukemia patients to adoptive cell transfer using autologous T cells genetically modified to express chimeric antigen receptors (CARs). However, the vast majority of cancers, in particular the more common solid cancers, such as those of the breast, colon and lung, fail to respond significantly to infusions of CAR T cells. Solid cancers present some formidable barriers to adoptive cell transfer, including suppression of T-cell function and inhibition of T-cell localization. In this review, we discuss the current state of CAR T-cell therapy in solid cancers, the variety of concepts being investigated to overcome these barriers as well as approaches aimed at increasing the specificity and safety of adoptive cell transfer.