Affiliations of authors: P. Stattin, Department of Urology and Andrology, Umeå University Hospital, Umeå, Sweden; R. Kaaks, Hormones and Cancer Group, International Agency for Research on Cancer, Lyon, France.
Correspondence to: Pär Stattin, M.D., Ph.D., Department of Urology, Umeå University Hospital, 901 85 Umeå, Sweden (e-mail: par.stattin{at}urologi.umu.se).
In three papers from the same casecontrol series recruited from Shanghai, China, Hsing et al. (13) have reported statistically significant associations between prostate cancer risk and aspects of insulin resistance syndrome. First, they observed an increase in prostate cancer risk associated with abdominal obesity, measured by waist-to-hip ratio (odds ratio [OR] = 2.71 for highest versus lowest quartile) (1). Subsequently, they reported an OR of 2.80 for highest versus lowest tertile of insulin (2), and they reported an OR of 2.78 for highest versus lowest tertile of an index of insulin resistance, calculated from fasting insulin and blood glucose levels in a homeostasis model (HOMA IR) (3). Equivalent results, but in the opposite direction, were found for an index of insulin sensitivity, instead of insulin resistance, calculated as "QUICKI." Hsing et al. pointed out the need for prospective studies on insulin resistance syndrome and prostate cancer risk.
Prompted by the work of Hsing et al. (13), we re-analyzed our data from The Northern Sweden Health and Disease Cohort, in which prostate cancer risk was not associated with body mass index (BMI) or insulin in blood samples collected, on average, 4 years before cancer diagnosis (4). We then calculated the ORs for indices of insulin resistance (HOMA IR) and insulin sensitivity (QUICKI), and we found no association between these indices or insulin levels and prostate cancer risk (Table 1). Given the strong correlation between insulin and HOMA IR (Spearman coefficient of correlation, r = .95) and between insulin and QUICKI (r = -.95) in our study, it is not surprising that all three measures resulted in very similar risk estimates.
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Possibly, prostate cancer risk is associated with insulin only at the lower end of the scale of insulin resistance and BMI, but not at levels common in subjects from Europe and the United States. BMI, a strong determinant of insulin resistance, has not been strongly associated with prostate cancer risk in Western populations (7). Alternatively, aggressive disease, which was more common in the Chinese study, may have a stronger association with hormonal changes than less aggressive disease. To what extent the results from the Chinese study subjects can be extrapolated to men in Western countries, or may explain the higher incidence rates in the West, remains to be elucidated.
REFERENCES
1 Hsing AW, Deng J, Sesterhenn IA, Mostofi FK, Stanczyk FZ, Benichou J, et al. Body size and prostate cancer: a population-based case-control study in China. Cancer Epidemiol Biomarkers Prev 2000;9:133541.
2 Hsing AW, Chua S Jr, Gao YT, Gentzschein E, Chang L, Deng J, et al. Prostate cancer risk and serum levels of insulin and leptin: a population-based study. J Natl Cancer Inst 2001;93: 7839.
3 Hsing AW, Gao YT, Chua S Jr, Deng J, Stanczyk FZ. Insulin resistance and prostate cancer risk. J Natl Cancer Inst 2003;95:6771.
4 Stattin P, Bylund A, Rinaldi S, Biessy C, Dechaud H, Stenman UH, et al. Plasma insulin-like growth factor-I, insulin-like growth factor-binding proteins, and prostate cancer risk: a prospective study. J Natl Cancer Inst 2000;92:19107.
5 Dennis LK, Resnick MI. Analysis of recent trends in prostate cancer incidence and mortality. Prostate 2000;42:24752.[CrossRef][ISI][Medline]
6 Online data for BMI in populations in the World Health Organizations Monitoring Trends in Cardiovascular Diseases (MONICA) Project. Available at: www.ktl.fi/publications/monica. [Last accessed May 27, 2003.]
7 Kaaks R, Lukanova A, Sommersberg B. Plasma androgens, IGF-I, body size and prostate cancer risk: a synthetic review. Prostate Cancer Prostatic Dis 2000;3:15772.[CrossRef][ISI][Medline]
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