Testicular cancer is a rare disease, accounting for 1.1% of all malignant neoplasms in Canadian males. Despite the low overall incidence of testicular cancer, it is the most common malignancy among young men. The incidence rate of testicular cancer has been increasing since the middle of the 20th century in many western countries. However, the etiology of testicular cancer is not well understood. A search of the peer-reviewed literature was conducted to identify important articles for review and inclusion in this overview of the epidemiology of testicular cancer. Most of the established risk factors are related to early life events, including cryptorchidism, carcinoma in situ and in utero exposure to estrogens. Occupational, lifestyle, socioeconomic and other risk factors have demonstrated mixed associations with testicular cancer. Although there are few established risk factors for testicular cancer, some appear to be related to hormonal balance at various life stages. Lifestyle and occupational exposures occurring later in life may play a role in promoting the disease, although they are not likely involved in cancer initiation. In addition to summarizing the current epidemiologic evidence on risk factors for testicular cancer, we suggest future research directions that may elucidate the etiology of testicular cancer. ' 2005 Wiley-Liss, Inc.Over the last 30 years, many studies have sought to discover factors associated with the development and promotion of testicular cancer. At present, however, there are few well-established risk factors for this disease, most notably cryptorchidism and age. For the most part, the etiology of testicular cancer remains unknown.This article provides an overview of risk factors that have been associated with testicular cancer to date. The purpose of this overview is to summarize the scientific literature on the epidemiology of testicular cancer, thereby providing a guide for future research that will advance our knowledge of testicular cancer etiology. Our overview is based on a detailed literature search dating to the late 1960s that was carried out through electronic databases and Medline. The publications considered in this overview are reliable scientific articles on the etiology of testicular cancer from different parts of the world. Incidence trendsThe worldwide incidence of testicular cancer has doubled over the last 40 years.1 In most countries, testicular cancer is rare, with an age-standardized incidence rate ranging from about 1/100,000 in Asian and African/African-American populations to 9.2/ 100,000 in Denmark (Table I).2 The age distribution of testicular cancer is distinct from that for other cancers, with the majority of cases occurring between the ages of 25-35.3 A second, much smaller, peak occurs after 80 years of age.3-5 Testicular cancer incidence varies markedly by race, with blacks and other nonwhite races exhibiting extremely low rates in comparison to white populations.

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