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Dr Eleanor Watts investigates the prostate cancer incidence and mortality risks associated with blood levels of insulin-like growth factor-1 and testosterone.

Globally, prostate cancer is the second most common cancer in men and kills over 350,000 men per year (World Health Organization). Understanding more about the risk factors for initiation, progression and mortality of this cancer may inform ways to reduce the risk, such as through diet, lifestyle and body size.

Previous work has confirmed an association between raised levels of insulin-like growth factor-1 (IGF-1) in the blood and prostate cancer. The blood levels of the hormone testosterone are also known to play a role in prostate cancer development. In particular, the levels of the biologically active freely circulating testosterone that is not bound to sex hormone-binding globulin (SHBG) and albumin show a positive association with prostate cancer risk. While these factors have been shown to be associated with prostate cancer diagnosis, less is known about their link to more aggressive prostate cancer subtypes.

To address this question, Dr Watts and colleagues analysed data from the UK Biobank. This is a national prospective cohort of over 500,000 participants recruited between 2006-2010. All participants had a blood sample taken at the start of the study and another 20,000 had a repeat measurement, allowing more precise risk estimates. Over an average follow-up of 7 years, 5,402 men went on to be diagnosed with prostate cancer and 295 died from the disease. The researchers were also able to account for other factors that can influence cancer risk, including body size, socioeconomic status and diabetes.

This work confirmed previously known links between serum IGF-1, SHBG and free testosterone concentrations and prostate cancer incidence. While neither serum SHBG nor free testosterone correlated with prostate cancer mortality, serum IGF-1 was positively associated with mortality. This suggests that IGF-1 may also increase the risk of developing more aggressive prostate cancer. The role of IGF-I in relation to prostate cancer diagnosis was also supported by a method called Mendelian randomisation, which can bypass some of the biases from observational studies by investigating whether the genes that are correlated with IGF-1 are also associated with prostate cancer.

This research was published in the International Journal of Cancer. Further work is now needed to examine hormone associations by tumour stage and grade.