Etiology of Lung Cancer among Women in Northern Thailand

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Nothern part of Thailand, in particular Chiang Mai Province, has been known to show very high incidence rates of lung cancer, which yearly increase, on the basis of the cancer registry data, i.e., the age-adjusted rates were 34.5 and 26.9 in 1985 for men and women, respectively ; those increased to 47.7 and 40.1 in 1992. Particularly, recent increase of lung cancer incidence in Chiang Mai women aged over 55 years is a serious problem to be solved along with the very high incidence of lung cancer as a whole. Only few studies have been so far carried out to find the causes of lung cancer and thus establish preventive measures against lung cancer.We started a research project on the etiology of lung cancer in collaboration with the faculty of medicine, Chaing Mai University, since 1995. This research project entailed the following three approaches :1) a comparative study of general women living in high and low incidence areas of lung cancer in Chiang Mai, 2) a case-control study at a hosp … More ital (Maharaj Nakorn Chiang Mai Hospital) of the faculty of medicine, Chiang Mai University, which is the largest hospital in Chiang Mai Province, and 3) pathological and molecular biological studies on lung cancer specimens obtained at the Maharaj Nakorn Chiang Mai Hospital.The first approach includes a epidemiological survey on their lifestyle by interviewing, nutritional survey on duplicated meals, serological analysis of their serum samples, mutagenicity assay of urine samples, identification of bacteria and fungi in sputum and those floating in the air indoor their houses. We surveyed 57 and 59 women aged at 50-74 years living at Sarapee (high incidence) and Chomtong (low incidence ; about the one-fourth of Sarapee's rate) districts in 1995 and 1996, respectively. Lower rate, 28.1%, of current smokers was observed in Sarapee, compared with 61.0% in Chomtong district.This result strongly implies that cigarette smoking alone can not explain the remarkable difference in lung cancer incidence between these districts. Althoug intake frequency and amount of green & yellow vegetables and fruits was less in Sarapee than that in Chomtong, the most outstanding difference between the districts was prevalence of benigh respiratory diseases : 43.7% in Sarapee experienced benigh respiratory diseases such as clonical bronchitis and COPD in contrast to 13.6% in Chomtong. Those female smokers in Sarapee who experienced benigh respiratory diseases showed very high serum IgE levels over 1000 U/ml, indicating long-term exposure of the lung to environmental substances. Furthermore, some types of bacteria, in particular M.canis, were specifically found in the air inside the houses in Sarapee.Along with the approaches 2) and 3), we isolated and cultured these bacteria for subsequent animal experiments to examine the tumor promotion activity of the bacteria. Less