Frequent loss of heterozygosity (LOH) at human chromosome 8p22-p21 is associated with various tumors including prostate and breast cancer. The 8p22-p21 region contains the FEZ1 gene, which is altered in tumors of the esophagus, prostate and breast. The FEZ1 protein (also known as leucine zipper putative tumor suppressor or LZTS1) contains a DNA-binding leucine zipper motif. FEZ1 is expressed in normal breast and prostate, but alterations in FEZ1 expression result in abnormal cell growth. The absence of FEZ1 expression is characteristic of breast and prostate cancer cell lines as well as primary breast and pro-state tumors. This absence of FEZ1 may be due to several factors, including mutations in the FEZ1 gene or hypermethylation of the CpG island flanking the FEZ1 promoter region. FEZ1 acts as a negative regulator of cell growth. During cell-cycle progression, FEZ1 localizes to microtubule components and is hyperphosphorylated by cAMP-dependent kinase.