KLF4 expression is reduced in several types of solid tumors. For example, KLF4 protein levels are decreased in more than 80 percent of colon tissues, compared to case-matched normal tissues. Induction of KLF4 expression in a colorectal cancer cell line results in diminished tumorigenicity. Also, more than 80 percent of lung tumor tissues have been shown to have decreased KLF4 protein levels compared to their case-matched normal tissues. In addition to colon and lung cancers, KLF4 serves as a tumor suppressor in bladder, gastric, esophageal, prostate and pancreatic cancers. Expression of KLF4 in cancer cell lines results in cell cycle arrest at G1/S due to increased expression of p27 and cyclin-dependent kinase inhibitor p21, both of which are induced by KLF4. Overexpression of KLF4 inhibits cancer cell proliferation through diverse mechanisms in solid tumors, including cell cycle arrest, induction of apoptosis and decreased metastasis.