Cancer in Chiang Mai, North Thailand. A relative frequency study.

The relative frequency of histologically diagnosed cancer at the Chiang Mai Medical School in North Thailand in 1964-67 inclusive is examined.Most of the 1877 cancers seen are in Thais (males, 927; females, 908), the remainder arising in Chinese (males, 21; females, 12), Hill People (males, 6; females, 1) and others (females, 2). The cancers in Thais are presented by site, sex and 10-year age-group together with the relative frequency (crude and corrected for age).In Thais, the outstanding finding is the extraordinarily high frequency of cancer of the hypopharyngeal-laryngeal region in both sexes (males, 18.4 per cent; females, 3.4 per cent). This may be associated with the smoking of a local variety of the cigar called "keeyo" This cigar, smoked in the usual manner, contains approximately equal quantities of home-grown, sun-dried, Thai tobacco and the chopped bark of the "koi" tree (Streblus asper). In women, who also smoke "keeyo", the frequency of hypopharyngeal-laryngeal cancer is unusually high by occidental standards. There is no sex difference in the frequency of bronchial cancer (4 per cent).In males cancer of the penis, in second rank (6.6 per cent) is much more frequent than cancer of the prostate and testis combined. Stomach and skin cancers (ICD 191) are in third place (each 5.7 per cent).In females the most frequent cancers are cervix uteri (19.8 per cent), breast (8.8 per cent) and skin (ICD 191) (6.1 per cent). Cancers of the lip and skin of the head and neck are more frequent in females than in males. Choriocarcinoma is common (1.9 per cent) and there is a large number of vulvar cancers in young women (2.6 per cent).The geography, economy and medical facilities of Chiang Mai Province are described. It is considered that, although there is likely to be considerable under-reporting of internal cancers, the high frequency of hypopharyngeallaryngeal cancer is not due to selective bias.