The genetic etiology of serous and mucinous ovarian carcinomas was investigated in 76 affected patients, focusing on the possible loss of heterozygosity (LOH) involving chromosome band 6q27 and K-RAS mutations at codon 12. The incidence of LOH in 6q27 (6q27 LOH) was 41% in 64 informative cases; 53% (20/38) and 23% (6/26) in cases of serous ovarian carcinoma and in those of mucinous ovarian carcinoma, respectively, indicating that the incidence of 6q27 LOH was significantly higher in cases of serous ovarian carcinoma (P < 0.05). The incidence of K-RAS mutations at codon 12 was 23% (15/64); 5% (2/38) and 50% (13/26) in cases of serous ovarian carcinoma and in those of mucinous ovarian carcinoma, respectively, indicating that the incidence of the K-RAS mutations was significantly higher in cases of mucinous ovarian carcinoma (P < 0.0001). Thus, K-RAS mutations at codon 12 and 6q27 LOH were suggested to be involved in the development and/or progression of mucinous ovarian carcinoma and serous ovarian carcinoma, respectively.

We report the complete genomic DNA sequence and the characterization of a 330-kb region on chromosome 6q27 that is often deleted in ovarian cancers. Using computer programs to predict exonic sequences, we isolated four novel genes, HGC6.1-4, as well as the known AF-6 gene. None of the deduced products of the novel genes exhibited significant homology to previously known proteins. We also identified ten microsatellites and 12 different VNTR sequences within the target region. HGC6.3 contained a VNTR within a coding exon, each repeat consisting of 42 nucleotides; the predicted 14-amino-acid consensus unit is MTPTVFSSQHTAGG. At least nine different sizes of this VNTR locus were detected among 20 unrelated DNA samples from caucasians. The polymorphic markers and the transcript map documented here may contribute to identification of novel genes or allelic aberrations associated with the development of ovarian cancers.

Allelic deletions of chromosome 6q that occur frequently in ovarian cancers imply the presence of a putative tumor suppressor gene in this chromosomal vicinity. We analyzed DNA from 32 patients with ovarian carcinomas for loss of heterozygosity at loci on the distal portion of chromosome 6q and constructed a detailed deletion map. The map indicated a commonly deleted region between loci D6S149 (defined by CI6-24) and A2, which are estimated to be 300 kb apart on the basis of our cosmid contig map. By means of exon trapping, we found that the human AF-6 gene, which is disrupted in acute myeloid leukemia cells that carry a (6;11)(q27;q23) translocation, is located within the commonly deleted region. Subsequent screening of the AF-6 gene in ovarian carcinomas revealed no mutations. However, our mapping results, which narrowed the region containing the putative tumor suppressor gene to a 300-kb segment of 6q27, will facilitate further efforts to identify a gene associated with ovarian cancer.

To define a small region on chromosome 6q containing a putative tumor suppressor gene for ovarian cancer, we examined loss of heterozygosity in 70 ovarian tumors of three histological types with nine restriction fragment length polymorphism markers located at 6q24-27. Among 33 cancers of serous type that were informative at one or more loci, 17 showed allelic loss at a few or all loci examined, whereas only 1 of 15 mucinous-type tumors and 2 of 12 clear-cell tumors revealed loss of heterozygosity. This result supported our earlier suggestion that alteration of a gene on chromosome 6q may play an important role during development of serous ovarian tumors (Sato et al., Cancer Res., 51: 5118-5122, 1991). Frequent losses were observed between loci defined by CI6-119 (D6S195) at 6q26 and CI6-49 (D6S161) at 6q27. A detailed deletion map indicated a commonly deleted region between loci defined by CI6-111 (D6S193) and CI6-24 (D6S149); these two markers are estimated to be 1.9 cM apart on the basis of linkage analysis. Our results further define a region containing a tumor suppressor gene involved in ovarian carcinoma within an approximately 2-megabase-long segment of chromosome 6q.