Cytogenetic and molecular genetic analyses of prostate cancer specimens have revealed nonrandom chromosomal deletions, affecting chromosomes 7q, 8p, 10q and 16q. Based on these data, we designed this study to further characterize the altered region(s) on chromosome 16 by evaluating 16 microsatellite markers on a population composed of 32 paired normal and primary prostatic tumor samples. The 16 microsatellites selected mapped to 11 distinct loci on 16q and 5 loci on 16p. No alterations were identified affecting 16p. However, 16 of 31 (51%) informative cases showed molecular alterations in at least one of the loci analyzed on 16q, consisting of 18 deletions and 11 bandshifts. Moreover, most of the deletions clustered at 6 microsatellite loci, mapping to the 16q22. Cytogenetic and molecular genetic analyses of prostate cancer have revealed consistent chromosomal alterations (Lundgren et al., 1992). Common sites of deletions have been reported for chromosomes 7q, 8p, 10q and 16q (Carter et al., 1990;Kunimi et al., 1991;Macoska et al., 1994). Nevertheless, the most frequent site of chromosomal losses in prostate cancer, together with 8p deletions, appears to be chromosome 16q Massenkeil et al., 1994;Philip et al., 1994). Loss of heterozygosity (LOH) at 16q was reported in 5 of 16 (31%) prostate cancer samples analyzed by restriction fragment length polymorphism (RFLP) and Southern blot (SB) analysis (Carter et al., 1990). These losses mapped to the 16q22.1-22.2 and 16q24.2 regions. Subsequently, Kunimi et al. (1991) reported 16q LOH in 6 of 10 (60%) informative prostatic carcinomas, mapping the losses to the HP locus at 16q22.1. Similarly, Bergerheim et al. (1991) reported that 10 of 18 prostate cancer cases (56%) studied had 16q deletions. However, a lower incidence of deletions was reported by Massenkeil et al. (1994). These investigators identified deletions at the 16q22-24 region in only 3 of 21 (15%) informative cases. Philip et al. (1994) found comparable results, detecting 16q24 deletions in 3 of 17 (18%) prostate carcinomas. In another study, 52 prostatic tumors were analyzed and an overall 16q deletion rate of 36% was reported . Moreover, this study also revealed that 16q losses were more commonly detected in metastatic lesions than in primary tumors. Taken together, these data suggest that the long arm of chromosome 16 harbors a candidate tumor suppressor gene (TSG) involved in prostate cancer progression. The chromosomal deletions described above were further confirmed using microsatellite repeat amplification. Sakr et al. (1994) identified allelic losses at 16q22.1 in a subset of primary prostate cancer (42% of informative cases). Gao et al. (1994) reported a high frequency of the mutator phenotype at 18 microsatellite marker loci on 12 chromosomes. A proximal locus on 16q11.2 showed alterations in 7 of 31 cases (23%). In addition, analysis of chromosome 16q using fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) revealed a higher incidence of deletions (Cher et al., 1...