Chromosome 18q is among the chromosomal regions thought to harbor a tumor suppressor gene(s) that is frequently inactivated during the development of several cancer types, particularly those of the gastrointestinal tract. Moreover, preliminary data suggest that colorectal cancers with 18q LOH have a more aggressive clinical behavior than those cancers without 18q LOH. A candidate tumor suppressor gene from 18q, termed DCC for deleted in colorectal cancer, has been identified. The DCC gene is contained within the common region of LOH on 18q, its expression is markedly decreased or absent in colorectal cancers and cell lines, and a subset of colorectal cancers have been shown to have somatic mutations within the DCC gene. Thus, DCC represents the most promising candidate tumor suppressor gene from 18q. At present, however, many questions remain regarding the mechanisms underlying the inactivation of DCC in the majority of colorectal cancers. In addition, although studies of 18q LOH and DCC gene expression in other cancer types suggest that DCC inactivation may contribute to the pathogenesis of other tumor types, few studies have provided definitive data to demonstrate that DCC inactivation is a critical genetic event in these tumors. Moreover, little is known about the function of DCC in the regulation of normal cell growth and tumor suppression. The predicted structural similarity of DCC to the N-CAM family of cell-surface proteins suggests that it may function through cell-cell and/or cell-extracellular matrix interactions.(ABSTRACT TRUNCATED AT 250 WORDS)