Summary Cancer of the oesophagus is the most commonly diagnosed cancer in males in Assam, in north-eastern India, and ranks second for females. The chewing of betel nut, with or without tobacco and prepared in various ways, is a common practice in the region and a case-control study has been designed to study the pattern of risk associated with different ways of preparing and chewing the nuts. 358 newly diagnosed male patients and 144 female have been interviewed together with 2 control subjects for each case chosen at random from among the attendants who accompanied patients to hospital. There were significant trends in risk ratios associated with the frequency of chewing each day, with the duration of chewing in years and with the age at which the habit was started that were apparent for both males and females and which remained significant after allowance was made for other known risk factors, notably tobacco smoking and alcohol consumption. The adjusted ratios, in comparison with non-chewers, were 13.3 M and 5.7 F for chewing more than 20 times a day, 10.6 M and 7.2 F for persons who had chewed for more than 20 years and 10.3 M and 5.3 F for those who had started before the age of 20. Among the different combinations of ingredients that were chewed the adjusted odds ratios were highest for those who had been using fermented betel nut with any form of tobacco (7.1 M and 3.6 F). The risk associated with tobacco smoking and alcohol consumption, which are high in some parts of the world, were less in Assam than those associated with the chewing of betel nut.

The etiology of esophageal cancer remains largely unknown. In recent years, the role of dietary habits in the development of esophageal cancer has received much attention. Prevalence of esophageal cancer in Assam is highest among all the states of India. To identify the possible risk factors, a hospital-based case-control study was conducted with 502 cases and 1,004 controls. "Kalakhar," a unique and locally made food item, has emerged as a significant risk factor (odds ratio = 8.0, 95% confidence interval = 5.1-11.5, p < 0.001). Consumption of very spicy foods, hot foods and beverages, a diet containing high amounts of chili, and leftover food was positively associated with the risk of esophageal cancer. Green leafy vegetables and fruits were protective for esophageal cancer. The risk factors associated with consumption of locally prepared food items, e.g., kalakhar, and some dietary practices did not decrease, even after adjustments with different confounding factors. However, further studies are required to conclusively implicate these factors in causation of esophageal cancer.