The epidemiology of pancreatic, gallbladder, and other biliary tract cancers.

Abstract

OVERVIEW Pancreatic cancer is the fifth leading cause of cancer-related death in the United States and will result in an estimated 29,700 deaths in 2002. In comparison, biliary tract cancer is rare, accounting for approximately 3500 deaths per year. The progression of pancreatic and biliary tract cancer often occurs without early symptoms, and diagnosis takes place late in the natural history of the disease. Consequently, both types of cancers have dismal survival rates, and treatment has little to no effect on prolonging the lives of these patients. The majority of pancreatic cancer arises in the exocrine pancreas. In the United States, incidence rates among men are approximately 1.3 times those among women, and blacks have 1.6 times the rates of whites. Incidence increases exponentially with age after 30 years old, and 80% of all cases are diagnosed between the ages of 60 and 80. Although pancreatic cancer incidence varies widely around the world, comparisons are challenging because of inconsistencies in diagnostic accuracy. However, industrialized nations appear to carry a higher burden of pancreatic cancer than less developed nations. In the past 2 decades, epidemiologic studies examining pancreatic cancer have been plagued with methodologic issues associated with studying a highly fatal disease, thereby hindering our understanding of the etiology of pancreatic cancer. Nevertheless, studies have consistently shown that tobacco smoking increases the risk of pancreatic cancer. Strong evidence also supports the association between pancreatic cancer and two medical conditions, chronic pancreatitis, and diabetes mellitus. Given that these conditions are often present numerous years before the cancer diagnosis, they should be considered as etiologically relevant. A series of recent studies indicate that obesity may be an important risk factor for pancreatic cancer. Other potential lifestyle risk factors include dietary factors such as carbohydrate and meat consumption, and physical activity. Biliary tract cancer can arise in the gallbladder or extrahepatic bile ducts. Gallbladder cancer is the most common of the two types and occurs more frequently in women than men. In contrast, extrahepatic bile duct cancer is seen more frequently in men. Although biliary tract tumors are relatively uncommon in the United States, certain ethnic groups, notably American Indians and Hispanic Americans, have substantially higher rates than the rest of the population. Gallstone disease is the most important risk factor for gallbladder cancer, increasing the risk by at least 3-fold. Because of the rarity of biliary tract tumors, diagnostic difficulties, and high mortality, other risk factors for this cancer are not well established. Among the potential risk factors are obesity, reproductive and hormonal factors, cholecystitis, biliary tract infections, and family history. Given the important epidemiologic dissimilarities of pancreaticobiliary cancers, correct classification is critical to improve the quality of epidemiologic studies. A better understanding of the underlying causes of these deadly cancers will provide new leads for early detection, treatment, and prevention. PANCREATIC CANCER Because the majority of pancreatic cancers occur in the exocrine pancreas, and tumors other than adenocarcinomas tumors are quite rare, this article will only focus on exocrine adenocarcinoma of the pancreas.