Loss of heterozygosity on chromosome 5 in Iranian esophageal cancer patients.

There is a high incidence of esophageal squamous cell carcinoma (ESCC) in Iran. Non-functionality of some tumor suppressor genes has been reported in esophageal cancer. Loss of heterozygosity on chromosome 5 has also been reported in esophageal carcinomas. We assessed loss of heterozygosity along a region of the long arm of chromosome 5 (5q), from 5q23.1 to 5q23.2, by PCR amplifying DNA fragments of tumor tissues from patients with ESCC and their corresponding normal samples. The PCR products were electrophoresed on 6% non-denaturing polyacrylamide gels, and band intensity was shown by silver staining. Of 40 patients with ESCC, 27, 25 and 36% of informative cases showed allelic losses at microsatellite markers D5S1384, D5S1478 and D5S1505, respectively. Two of the 40 patients studied had microsatellite instability at marker D5S1384. Based on the fact that loss of heterozygosity with more than 22% incidence for a specific marker cannot be regarded as a random event, we add support to previous reports concerning the presence of tumor suppressor genes in this chromosome region and that they affect esophageal cancer development. According to the data in NCBI UniSTS, the PCR product size of human DNA with primers of the D5S1505 marker ranges from 243 to 275 bp, containing about 20 repeats of the TAGA tetranucleotide, while the amplicon size of one allele of one of our cases was 207 bp, with about 10 repeats of the TAGA tetranucleotide, which would be the shortest sequence reported so far.

Associations of risk factors obesity and occupational airborne exposures with CDKN2A/p16 aberrant DNA methylation in esophageal cancer patients.

It is known that obesity and occupational airborne exposure such as dust are among risk factors of esophageal cancer development, in particular squamous cell carcinoma (SCC) of esophagus. Here, we tested whether these factors could also affect aberrant DNA methylation. DNAs from 44 fresh tumor tissues and 19 non-tumor adjacent normal tissues, obtained from 44 patients affected by SCC of esophagus (SCCE), were studied for methylation at the CDKN2A/p16 gene promoter by methylation-specific polymerase chain reaction assay. Statistical methods were used to assess association of promoter methylation with biopathological, clinical, and personal information data, including obesity and airborne exposures. Methylation at the CDKN2A/p16 gene promoter was detected in 12 out of 44 tumor samples. None of the non-tumor tissues exhibited the aberrant methylation. Our results confirmed previously described significant association with low tumor stage (P= 0.002); in addition, we found that obesity (P= 0.001) and occupational exposure (P= 0.008) were both significantly associated with CDKN2A/p16 promoter methylation. This study provides evidence that obesity and occupational exposure increase the risk of developing esophageal cancer through an enhancement of CDKN2A/p16 promoter methylation.

Distinct pattern of TP53 mutations in squamous cell carcinoma of the esophagus in Iran.

Extremely high rates of squamous cell carcinoma of the esophagus (SCCE) are observed in Iran, reflecting unknown, genetic and/or epidemiological risk factors. Among genetic alterations in SCCE, TP53 mutations are the most frequent, vary among populations, and may provide clues on etiological mechanisms. We have analysed mutations in TP53 (exons 5-8) in 98 SCCE from Iran by temporal temperature gel electrophoresis and direct sequencing. We found 58 mutations in 49 patients (50%), with a high prevalence of C to T transitions at CpG dinucleotides (29.3%). The TP53 mutation pattern in Iran was significantly different from that observed in SCCEs from high incidence areas of China and Western Europe (P=0.007). Moreover, the prevalence of mutations at A : T base pairs (transitions and transversions) was higher in men than in women (38.7% vs 11.1%, P=0.033). COX-2 overexpression was detected in 69% of the cases evaluated (24/35), without significant association with TP53 mutation. Accumulation of nitrotyrosine, a marker of protein damage by excess levels of nitric oxide, was observed in tumor cells in six of 18 [corrected] cases analysed. These results are consistent with the hypothesis that several factors are involved in TP53 mutagenesis in Iran. These factors include a baseline of chronic inflammatory stress, which may have a multiplicative impact on the sensitivity of esophageal cells to exogenous factors of risk.

Oesophageal cancer among the Turkomans of northeast Iran.

A Caspian Littoral Cancer Registry survey in the early 1970s established northern Iran as one of the highest oesophageal cancer incidence regions of the world. To verify this, an oesophageal cancer survey was carried out between 1995 and 1997 in the Turkoman Plain at the southeastern corner of the Caspian Sea. Oesophageal balloon cytology screening was carried out on 4192 asymptomatic adults above age 30 years in one town and three adjoining villages with a total population of 20 392 people at risk. Oesophagoscopy was performed on 183 patients with abnormal cytological findings. The discovery of two asymptomatic small squamous cell cancers and one 'carcinoma- suspect' implied a prevalence ranging from 47.7 per 100 000 to 71.5 per 100 000. During a 1-year active surveillance, 14 patients were found with clinically advanced oesophageal squamous cell cancer, yielding age-standardized incidence rates of 144.09 per 100 000 for men and 48.82 per 100 000 for women. The very high frequency of oesophageal cancer reported for northern Iran 25 years ago stands confirmed. Differences in incidence rates, then and now, can be attributed to survey methods used and diagnostic criteria applied, but not to socioeconomic factors, which have remained relatively stable. Oesophageal balloon cytology is a practical method of mass screening for oesophageal cancer in Iran.