The present invention relates to a new tumor suppressor, designated CAR-1, the gene for which is located on the short arm of human chromosome 1. This gene is directly implicated in colon, kidney and breast cancers, and the CAR-1 ubiquitous expression of the corresponding transcript suggests that it may be involved in yet others. Thus, one aspect of the invention is the diagnosis of CAR-1-related malignancies. The full length cDNA for CAR-1, as well as oligonucleotides derived therefrom, are disclosed. Screening methods for modulators of CAR-1 function and expression, as well as methods for cancer therapy, are described.