The B7 family consists of activating and inhibitory co-stimulatory molecules that positively and negatively regulate immune responses. An imbalance in immune regulation profoundly affects tumor-specific T-cell immunity in the cancer microenvironment and can reshape tumor progression, metastasis and immunotherapy in patients with cancer. B7-H1 and B7-H4 molecules provide negative signals that control and suppress T-cell responses. Human tumor cells and tumor-associated APCs express limited levels of the stimulatory B7-family members CD80 and CD86, and high levels of the inhibitory B7-family members B7-H1 and B7-H4. This imbalance between the expression of stimulatory and inhibitory B7 molecules might contribute to tumor immune evasion in the tumor microenvironment.