Original Article: Clinical Investigation Diabetes mellitus and kidney cancer risk: The results of Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) Masakazu Washio, 1,2 Mitsuru Mori, 1 Mmh Khan, 1 Fumio Sakauchi, 1 Yoshiyuki Watanabe, 3 Kotaro Ozasa, 3 Kyohei Hayashi, 3 Tsuneharu Miki, 4 Masahiro Nakao, 4 Kazuya Mikami, 4 Yoshinori Ito, 5,8 Tatsuhiko Kubo, 6 Kenji Wakai 7,8 and Akiko Tamakoshi 8 For The JACC Study Group 1 Department of Public Health, Sapporo Medical University School of Medicine, Sapporo, 2 Department of Community Health and Clinical Epidemiology, St. Mary’s College, Fukuoka, 3 Department of Epidemiology for Community Health and Medicine, Kyoto Prefectural University of Medicine, 4 Department of Urology, Graduate School of Medical Sciences, Kyoto Prefectural University of Medicine, Kyoto, 5 Department of Public Health, Fujita Health University School of Health Sciences, Fujita, 6 Department of Clinical Epidemiology, University of Occupational Health and Environmental Health, Kitakyushu, 7 Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute, Aichi, 8 Department of Preventive Medicine/Biostatistics and Medical Decision Making, Nagoya University Graduate School of Medicine, Nagoya, Japan Background: Diabetes mellitus (DM) is reported as being a risk factor associated with kidney cancer in Western countries. The incidence of both kidney cancer and DM is lower in Japan than the other developed countries, albeit on the rise. Methods: We evaluated the risk factors for kidney cancer mortality using the database of the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC) study. The analytic cohort included 46 462 males and 64 326 females aged 40–79 years old. The Cox proportional hazards model was used to determine age- and sex-adjusted relative risk and its 95% confidence intervals. Results: DM showed an increased, age- and sex-adjusted hazard ratio for kidney cancer mortality, but it failed to achieve statistical significance after controlling for other factors. Conclusion: The present study showed that DM increased the risk of kidney cancer death among the Japanese population. However, further studies may be needed to confirm the findings in the present study because DM failed to remain as a significant risk factor after controlling for other factors because of the small number of kidney cancer deaths in the present study. Key words: diabetes mellitus, Japan, renal cell carcinoma, risk factor. Introduction The incidence of kidney cancer 1–3 is high in Europe and North America whereas it is low inAsia. However, the incidence of kidney cancer is higher among Japanese Americans than it is in native Japanese, 4 sug- gesting that Japanese people suffer from kidney cancer at a higher rate when immersed in Western culture. Although the incidence of kidney cancer is lower in Japan than in other industrialized countries, 1–4 there is no doubt that it has been increasing. 5 The Japanese lifestyle, including dietary habits, has changed in recent years. 6,7 The change in lifestyle including Western- ized dietary habits and the increase in ownership and usage of cars and household electric appliances, may have increased the prevalence of obesity. Obesity is a major risk factor associated with diabetes mellitus (DM) 8,9 and the incidence of DM increases according to body mass index (BMI). 8 Ohmura et al. 10 reported an increased frequency of DM, 10 and the incidence and mortality rate associated with kidney cancer 5 have also been increasing in recent years in Japan. An increased risk of kidney cancer has been reported among obese persons 11–15 as well as DM patients. 16,17 In 1991, Hirata 18 explained that the prevalence of obesity is much lower among Japanese DM patients than Caucasian DM patients, and most Japanese DM patients reduced their weight after being treated for DM. Although the precise mecha- nism of how obesity contributes to insulin resistance and DM has not yet been identified , 9 both DM and obesity are associated with hyper- insulinemia. 9,19 Therefore, in the present study, obese subjects without DM were categorized as ‘obesity without DM’. The present study focuses on the association between DM and kidney cancer mortality as well as obesity without DM and kidney cancer mortality among the Japanese population. Subjects and methods The Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) is a nationwide collaborative prospective cohort study to evaluate the various risks and/or protective factors influencing cancer mortality and incidence. 20 Study methods and ethical issues have been described elsewhere. 20 Briefly, the cohort was established 1988–1990, with 46 465 males and 64 327 females aged 40–79 years in 45 study areas across Japan. Most subjects were recruited from the general population or when undergoing routine municipal health checks. At the baseline survey, the participants completed a self-administrated ques- tionnaire containing questions on medical history, height and weight in addition to lifestyle factors such as smoking and drinking. Most study subjects (86.9%) were followed up for mortality until the end of 2003, Correspondence: Masakazu Washio MD, Department of Community Health and Clinical Epidemiology, St. Mary’s College, 422 Tsubuku-hon-machi, Kurume City, Fukuoka 830-8558, Japan. Email: washio@st-mary.ac.jp Received 16 June 2006; accepted 14 December 2006. International Journal of Urology (2007) 14, 393–397 doi: 10.1111/j.1442-2042.2007.01744.x © 2007 The Japanese Urological Association 393