In the United States, squamous cell carcinoma of the esophagus is strongly associated with tobacco and alcohol abuse. The risk declines with smoking cessation. In China, esophageal cancer is associated with deficiencies of nutrients such as retinol, riboflavin, alpha-carotene and beta carotene, alpha-tocopherol, ascorbate, and zinc, and with exposure to specific carcinogens (e.g., N-nitroso compounds).
A prospective, placebo-controlled, esophagus chemoprevention study randomly assigned 610 high-risk Chinese subjects. Subjects ranged in age from 35 to 64 years and received either placebo or combined low-dose retinol (15 mg or 50,000 IU) plus riboflavin (200 mg) and zinc gluconate (50 mg) for 13.5 months. Standard histological evaluations (including two endoscopic biopsies) were made of 93% of all entered subjects. Micronuclei from esophageal cells were obtained before therapy began and after the 13.5 months of treatment. Serum levels of vitamin A, beta carotene, riboflavin, and zinc were obtained at 0, 2, and 13.5 months.
The second report of this study presented micronuclei frequency results. A statistically significant reduction occurred in the mean percentage of micronucleated esophageal cells in the active-treatment group compared with the placebo group. The pattern of cell proliferation, another potential intermediate endpoint marker, also improved.
Two National Cancer Institute-sponsored phase III trials of combinations of multiple vitamins and minerals have been reported. Both were conducted in a high-risk area of China (Linxian). In one, a complex modified factorial design was used to study four different vitamin/mineral combinations administered for 5 years at doses one to two times the U.S. recommended daily allowances (RDA) to 29,584 subjects. The combination of beta carotene, alpha-tocopherol, and selenium was associated with a nonstatistically significant 4% reduction in the esophageal cancer mortality rate. The other trial included only higher-risk subjects with esophageal dysplasia  and had a two-arm design (26 vitamins and minerals, including beta carotene, alpha-tocopherol, and selenium, at two to three times the U.S. RDA in one arm versus placebo in the other). This 6-year intervention was associated with a nonsignificant change: a 16% reduction in the esophageal cancer mortality rate. Similar studies have not been conducted in the United States.