Hutcha Sriplung

The incidence of liver cancer varies widely throughout the world, with high rates in sub - Saharan Africa, eastern and southeastern Asia, and Melanesia and a low incidence in Northern and Western Europe and the Americas. Primary cancers of the liver in adults are of two main histological types: hepatocellular carcinoma, which is derived from hepatocytes, and cholangiocarcinoma, which is derived from the epithelial lining of the intrahepatic bile ducts. Hepatocellular cancer is a frequently occurring tumor in individuals in many developing countries, where several important risk factors have been demonstrated, including chronic infection with hepatitis B and C viruses and other environmental factors, such as exposure to aflatoxin, consumption of alcohol, and cigarette smoking. By contrast, cholangiocarcinoma is less common, accounting for only 7.7% of malignant tumors of the liver in the United States. However, in parts of Southeast Asia, cholangiocarcinoma occurs more frequently; it is responsible for more than 60% of liver tumors in northeastern Thailand. The geographic distribution worldwide coincides with endemic areas of the liver flukes, Opisthorchis viverrini and Clonorchis sinensis. The interaction between genes and the environment and the interplay of environmental factors, which include diet and other lifestyle parameters, illustrate the complexity underlying susceptibility.

Infection with Opisthorchis viverrini (OV) is associated with cholangiocarcinoma. OV is common in northeast Thailand, but less than 10% of the inhabitants develop cholangiocarcinoma. Animal experiments suggest that OV infection alone does not cause cholangiocarcinoma, and thus other environmental and genetic factors may play a role in causation. We conducted a population-based case-control study in which sex, age and place of residence were matched individually. Polymorphisms of GSTM1 and GSTT1 alone were not associated with risk for cholangiocarcinoma, while an elevated level of antibodies against OV (ELISA) > or = 0.200 was the strongest risk indicator (odds ratio as compared to that <0.200 = 27.09 [95% confidence interval (CI): 6.30-116.57]. Compared to subjects who had a normal antibody range and the wild-type GSTM1 gene, those who had elevated antibodies had higher odds ratios of 10.34 (95% CI: 1.31-81.63) [corrected] for wild-type GSTM1 and 18.00 (95% CI: 3.33-97.40) [corrected] for the null variant thereof, respectively. Past and current regular drinkers of alcohol had higher risk [odds ratio = 5.39 (95% CI: 1.11-26.06) and 4.82 (95% CI: 1.29-18.06), respectively]. Eating fermented products was an independent risk factor. Smokers or consumers of fermented fish had substantially increased risk if they were past or current drinkers. Infection with OV correlates strongly with cholangiocarcinoma, susceptibility to which may be possibly associated with GSTM1 polymorphism. Alcohol may affect metabolic pathways of endogenous and exogenous nitrosamines.

Results from three cancer registries (Chiang Mai, Khon Kaen, and Songkhla) in different regions of Thailand and from a cancer survey in the population of Bangkok during the years 1988-1991 are presented, together with an estimate of the incidence of cancer for the country as a whole. Overall, liver cancer is the most frequent malignancy, but there are large regional differences in incidence and in histological type, with very high rates of cholangiocarcinoma in the northeast (associated with endemic opisthorchiasis) but a more even distribution of hepatocellular carcinoma. Lung cancer is second in frequency, with the highest rates in northern Thailand, where the incidence in women (Age Standardized Rate, 37.4 per 100,000) is among the highest in the world. A link with tobacco smoking is suggested by similarly raised rates, especially in women, for cancers of the larynx and pancreas. Cervical cancer is the most common malignancy in women, with relatively little regional variation in risk, while the incidence of breast cancer is low. Other cancer sites showing moderately increased rates include the lip and oral cavity, particularly in females from the north and northeast, where the chewing of betel nut remains common among older generations, nasopharyngeal cancer, carcinoma of the esophagus in the southern region, and penile cancer, especially in the north and northeast. Previous studies which have investigated the etiological factors underlying these patterns are reviewed, and the implications for future research and for national cancer control policies are discussed.

In Thailand, five cancer types-breast, cervical, colorectal, liver and lung cancer-contribute to over half of the cancer burden. The magnitude of these cancers must be quantified over time to assess previous health policies and highlight future trajectories for targeted prevention efforts. We provide a comprehensive assessment of these five cancers nationally and subnationally, with trend analysis, projections, and number of cases expected for the year 2025 using cancer registry data. We found that breast (average annual percent change (AAPC): 3.1%) and colorectal cancer (female AAPC: 3.3%, male AAPC: 4.1%) are increasing while cervical cancer (AAPC: -4.4%) is decreasing nationwide. However, liver and lung cancers exhibit disproportionately higher burdens in the northeast and north regions, respectively. Lung cancer increased significantly in northeastern and southern women, despite low smoking rates. Liver cancers are expected to increase in the northern males and females. Liver cancer increased in the south, despite the absence of the liver fluke, a known factor, in this region. Our findings are presented in the context of health policy, population dynamics and serve to provide evidence for future prevention strategies. Our subnational estimates provide a basis for understanding variations in region-specific risk factor profiles that contribute to incidence trends over time.