The cadherin family of cell adhesion molecules has been implicated in tumor metastasis and progression. Eight family members have been mapped to the long arm of chromosome 16. Using radiation hybrid mapping, we have located six of these genes within a cluster at 16q21-q22.1. In invasive lobular carcinoma of the breast frequent LOH and accompanying mutation affect the CDH1 gene, which is a member of this chromosome 16 gene cluster. CDH1 LOH also occurs in invasive ductal carcinoma, but in the absence of gene mutation. The proximity of other cadherin genes to 16q22.1 suggests that they may be affected by LOH in invasive ductal carcinomas. Using the mapping data, microsatellite markers were selected which span regions of chromosome 16 containing the cadherin genes. In breast cancer tissues, a high rate of allelic loss was found over the gene cluster region, with CDH1 being the most frequently lost marker. In invasive ductal carcinoma a minimal deleted region was identified within part of the chromosome 16 cadherin gene cluster. This provides strong evidence for the existence of a second 16q22 suppressor gene locus within the cadherin cluster.