Amplified in breast cancer-1 glutamine repeat and prostate cancer risk

Objectives: Amplified in breast cancer-1 (AIB1) is a steroid receptor coactivator that enhances estrogen-dependent transcriptional activation by the estrogen receptor. It is unknown whether AIB1 also interacts with the androgen receptor. Because the development and progression of prostate cancer is likely to be partially mediated by steroid hormones, we investigated whether a polymorphic CAG/CAA repeat encoding glutamine in the AIB1 gene is related to prostate cancer risk in a nested study of 581 patients and 786 age-matched control subjects in the Physicians' Health Study. Materials and Methods: DNA was extracted from peripheral whole blood, and the region encompassing the repeat was amplified using fluorescent-labeled primers. The fragments were run on polyacrylamide gels and sized by computer software. We estimated the relative risk (RR) of prostate cancer for AIB1 glutamine repeat length from logistic regression models controlling for the matching variables. Results: Three glutamine repeat lengths were prevalent: 29 (47.8% among control subjects), 28 (38.5% among control subjects), and 26 (12.6% among control subjects). Compared to 29 repeats, the RR of prostate cancer was 0.92 (95% confidence interval [CI] 0.72-1.17) for 26 repeats and 1.01 (95% CI 0.86-1.19) for 28 repeats. Compared to 28/29, the RR of prostate cancer was not significantly altered for any of the other common genotypes. No clear associations were present for AIB1 glutamine repeat length genotype by stage at the diagnosis/histologic grade of the tumor. Conclusion: This study does not support an important role in prostate cancer incidence or aggressiveness of AIB1 glutamine repeat length in the range observed in this predominately white cohort.