Epidemiology of digestive tract cancers in India. V. Large and small bowel

The large bowel is a leading site for cancers in developed countries whereas small bowel cancers are rare worldwide. The incidence rates of both large and small bowel cancer are low in India, and rectal cancer is more common than colon cancer. The incidence rates of colon cancer in eight population registries vary from 3.7 to 0.7/100,000 among men and 3 to 0.4/100,000 among women. For rectal cancer the incidence rates range from 5.5 to 1.6/100,000 among men and 2.8 to 0/100,000 among women. One intriguing observation is the occurrence of rectal cancer in young Indians. Rural incidence rates for large bowel cancers in India are approximately half of urban rates. Based on data from eight registries, we estimate that, in the year 2001, the incidence of large bowel cancer in India will be 18,427 in men and 13,092 in women. Immigrant studies reveal an increase in incidence as compared to the rates in native counterparts. Reliable time trends for India are available only from the Bombay registry. Significant increase in the incidence of colon cancer has been reported for both men and women over two decades, but the rates of rectal cancer are steady. The low incidence of large bowel cancers in Indians can be attributed to high intake of starch and the presence of natural antioxidants such as curcumin in Indian cooking. The role of hereditary factors has been evaluated in a few studies. Some studies have reported the occurrence of both FAP and HNPCC in India. There are no Indian studies on large bowel cancer prevention. The prevalence of adenomas is rare in elderly Indians undergoing colonoscopy, even in those with large bowel cancers. Small bowel cancers are extremely rare in India and no analytical studies have been published. Hospital-based data suggest that lymphomas of small bowel are more common than carcinomas. In conclusion, the incidence of large and small bowel adenomas and cancers is low in Indians. Increase in the incidence of large bowel cancers in immigrants and urban Indians compared to rural populations supports a role for environmental risk factors including diet. High rates of rectal cancers in young Indians could suggest a different etiopathogenesis, which is neither inherited nor traditional diet-related.