PPARG and neoplasm: Our experiments reveal that tumor cell proliferation could be significantly enhanced by co-culture with PPARγ-deficient macrophages but not by the conditioned medium from PPARγ-deficient macrophages (Figure 3A–B), indicating that physical contact between macrophages and cancer cells may be required and thus the key tumor-modulating PPARγ target gene in macrophages likely encodes a membrane protein.