Epidemiologic study of cancer in the gastrointestinal tract has brought out certain significant points: In India the frequency rate for cancer of the esophagus is very high. Stomach, colon and rectum are less affected. The proportion of squamous ceIl carcinoma of the anal canaI is quite high. The differences in the distribution of cancer within the esophagus at certain anatomical sites are studied. A preliminary analysis of the habit of smoking and chewing of pan indicates a significant association of the habit of smoking with cancer of the upper and middle portions of the esophagus whereas the lower third does not show this association. Different groups of population or communities in India show variations in the frequency of cancer in the gastrointestinal tract as well as in portions of the esophagus and such variations have a bearing on the habits and other associated factors prevalent in the members of these communities.
PIDEMIOLOGY OF CANCER DEALS WITH THE RE-
E lationship of various factors which determine the frequencies and the distributions of the disease in the human race. Its purpose is to discover the causes of the disease as well as the causes which lead to freedom from the disease with the ultimate aim to a better understanding of treatment and prevention.
T h e alimentary tract, which extends from the lips to the anus, is a common site for the development of malignant neoplasms in many countries of the world. The incidence of cancer in the entire tract or parts of it varies from place to place. In the majority of Western countries the disease occurs more often in that part of the tract which extends from the stomach downwards. Cancer of the stomach occurs in large proportions in Japan,24 Poland and Norway.27 T h e rate of cancer in the large intestine is higher in the United States and also in the United Kingdom in comparison with that in many other c o u n t r i e ~~7 In Japan and in India the proportion of cancer iq the rectum is comparatively higher than that recorded in the large intestine. The frequency of cancer in the anal canal is quite high in India.