Human cancers frequently show a loss of heterozygosity on chromosome 7q31, which indicates the existence of broad-range tumour-suppressor gene(s) at this locus. Truncating mutations in the ST7 gene at this locus are seen frequently in primary colon cancer and breast cancer cell lines. Therefore, the ST7 gene represents a novel candidate gene for the tumour suppressor at this locus. However, more recent studies have reported that ST7 mutations are infrequent or absent in primary cancer and cell lines. To ascertain the frequency of mutations of the ST7 gene in cancer cells, we examined mutations in the ST7 coding sequence in 48 colorectal, 48 gastric, and 48 hepatocellular carcinomas using polymerase chain reaction -single-strand conformational polymorphism and direct sequencing. We detected somatic mutations, which were located near the exon -intron junction in intron 8, in only three out of 144 cases. We conclude that mutations in the ST7 gene are rare in primary colorectal, gastric, and hepatocellular carcinomas. (Zenklusen et al, 2001). These results suggest that the ST7 gene is a candidate tumour-suppressor gene within this critical region. However, there have been reports that somatic mutation in the ST7 gene is extremely rare (Hughes et al, 2001;Thomas et al, 2001;Brown et al, 2002;Dong and Sidransky, 2002). Thus, the previous data on ST7 gene mutations show conflicting results.In this study, we investigated the true frequency of ST7 gene mutations by examining 48 primary colorectal cancers, 48 primary gastric cancers that frequently show LOH on 7q31 (Nishizuka et al, 1997), and 48 primary hepatocellular carcinomas that show highlevel expression of the ST7/RAY1 gene (Vincent et al, 2000;Zenklusen et al, 2001). We surveyed mutations in the entire ST7 coding sequence using polymerase chain reaction -single-strand conformational polymorphism (PCR -SSCP) analysis and direct DNA sequencing.
MATERIALS AND METHODS
Tissue specimens and DNA extractionSpecimens from 48 colorectal, 48 gastric, and 48 hepatocellular carcinomas and corresponding noncancerous tissues were obtained at surgery from Japanese patients. The samples were frozen immediately in liquid nitrogen and stored at À801C until use. High-molecular-weight DNA was extracted using the standard phenol/chloroform procedure.
