IGF1 and prostate cancer: We hypothesized that the inverse association between serum IGF‐1 level and tumor grade is due to the autonomy of high‐grade prostate cancer, similar to the inverse relationship between testosterone availability and high‐grade disease.19, 20, 21, 22, 23 To test this hypothesis, we assessed the relationship between serum IGF‐1 levels and testosterone levels, and found that the serum testosterone level itself is inversely proportional to the IGF‐1 level (r = −0.123; Figure 1A), but the bioavailable testosterone level is positively correlated with IGF‐1 (r = 0.157; Figure 1B).