Prognostic and predictive importance of the estrogen receptor coactivator AIB1 in a randomized trial comparing adjuvant letrozole and tamoxifen therapy in postmenopausal breast cancer: the Danish cohort of BIG 1-98.

PURPOSE: To evaluate the estrogen receptor coactivator amplified in breast cancer 1 (AIB1) as a prognostic marker, as well as a predictive marker for response to adjuvant tamoxifen and/or aromatase inhibitors, in early estrogen receptor-positive breast cancer. METHOD: AIB1 was analyzed with immunohistochemistry in tissue microarrays of the Danish subcohort (N = 1396) of the International Breast Cancer Study Group's trial BIG 1-98 (randomization between adjuvant tamoxifen versus letrozole versus the sequence of the two drugs). RESULTS: Forty-six percent of the tumors had a high AIB1 expression. In line with previous studies, AIB1 correlated to a more aggressive tumor-phenotype (HER2 amplification and a high malignancy grade). High AIB1 also correlated to higher estrogen receptor expression (80-100 vs. 1-79%), and ductal histological type. High AIB1 expression was associated with a poor disease-free survival (univariable: hazard ratio 1.35, 95% confidence interval 1.12-1.63. Multivariable: hazard ratio 1.29, 95% confidence interval 1.06-1.58) and overall survival (univariable: hazard ratio 1.34, 95% confidence interval 1.07-1.68. Multivariable: hazard ratio 1.25, 95% confidence interval 0.99-1.60). HER2 did not seem to modify the prognostic effect of AIB1. No difference in treatment effect between tamoxifen and letrozole in relation to AIB1 was found. CONCLUSIONS: In a subset of the large international randomized trial BIG 1-98, we confirm AIB1 to be a strong prognostic factor in early breast cancer. Hence, although tumor AIB1 expression does not seem to be useful for the choice of tamoxifen versus an aromatase inhibitor in postmenopausal endocrine-responsive breast cancer, AIB1 is an interesting target for new anti-cancer therapies and further investigations of this biomarker is warranted.

The role of AIB1 and PAX2 in primary breast cancer: validation of AIB1 as a negative prognostic factor.

Background The steroid-receptor coactivator amplified in breast cancer one (AIB1) is implicated to be a prognostic factor, although the results are not unanimous. Recently its effect was suggested to be modified by paired box 2 gene product (PAX2). Patients and methods Using immunohistochemistry (IHC) AIB1 and PAX2 were investigated in two cohorts of early breast cancer, including systemically untreated premenopausal lymph-node-negative women and pre- and postmenopausal women receiving tamoxifen. Results AIB1 scores were available for 490 patients and PAX2 scores were available for 463 patients. High AIB1 was a negative prognostic factor for distant disease-free survival (DDFS, P = 0.02) and overall survival (OS, P < 0.001) in systemically untreated women, while no prognostic effect was seen in the tamoxifen-treated cohort, indicating AIB1 to be a predictor of tamoxifen response. In systemically untreated patients, PAX2 was not a prognostic factor, nor did it modify the effect of AIB1. However, in ER-positive patients receiving tamoxifen, PAX2 appeared to be a positive prognostic factor in premenopausal patients, while a negative factor in postmenopausal. The interaction between the menopausal status and PAX2 was significant (P = 0.01). Conclusions In an independent cohort of low-risk premenopausal patients, we validate AIB1 as a negative prognostic factor, indicating AIB1 to be an interesting target for new anti-cancer therapies. The effect of PAX2 warrants further studies.

AIB1 is a predictive factor for tamoxifen response in premenopausal women.

BACKGROUND: Clinical trials implicate the estrogen receptor (ER) coactivator amplified in breast cancer 1 (AIB1) to be a prognostic and a treatment-predictive factor, although results are not unanimous. We have further investigated this using a controlled randomised trial of tamoxifen versus control. MATERIALS AND METHODS: A total of 564 premenopausal women were entered into a randomised study independent of ER status. Using a tissue microarray, AIB1 and ER were analysed by immunohistochemistry. RESULTS: AIB1 scores were obtained from 349 women. High AIB1 correlated to factors of worse prognosis (human epidermal growth factor receptor 2, Nottingham histological grade 3, and lymph node metastases) and to ER negativity. In the control arm, high AIB1 was a negative prognostic factor for recurrence-free survival (RFS) (P = 0.02). However, ER-positive patients with high AIB1 responded significantly to tamoxifen treatment (P = 0.002), increasing RFS to the same level as for systemically untreated patients with low AIB1. Although ER-positive patients with low AIB1 had a better RFS from the beginning, this was not further improved by tamoxifen (P = 0.8). CONCLUSIONS: In the control group, high AIB1 was a negative prognostic factor. However, ER-positive patients with high AIB1 responded significantly to tamoxifen. This implicates high AIB1 to be an independent predictive factor of improved response to tamoxifen and not, as has previously been discussed, a factor predicting tamoxifen resistance.