Cyclin D1 expression in breast cancer patients and tamoxifen therapy

Abstract

523 Background: Adjuvant tamoxifen therapy improves survival of hormone receptor-positive breast cancer patients, but there is a subset of patients who fails to respond or develops resistance to tamoxifen. Cyclin D1 plays a central role in cell cycle regulation, directly affects the estrogen receptor and may predict outcome of tamoxifen therapy. Methods: We determined expression of cyclin D1 in formalin-fixed, paraffin-embedded surgical breast cancer specimens by means of immunohistochemistry. The patients had been enrolled in the Austrian Breast and Colorectal Cancer Study Group (ABCSG) Trial 5 (test set) or ABCSG Trial 6 (validation set). Comparison of cyclin D1 expression with clinical parameters and survival of the patients was performed with cyclin D1 as a continuous variable and as a dichotomized variable. The median value of the percentage of cyclin D1-positive tumor cells was a priori chosen as cut-off point to classify cyclin D1- positive and cyclin D1-negative tumors. The cutpoint was established in the test set and validated in the validation set. Overall survival and relapse-free survival were analyzed with Cox models adjusted for clinical and pathological factors. Results: Cyclin D1 was positive (>10% cyclin D1-positive tumor cells) in 140 of 253 (55%) tumors of the test set and in 569 of 948 (60%) tumors of the validation set. A benefit from adjuvant endocrine therapy was associated with absence of cyclin D1 in both cohorts. Overall survival was significantly shorter in patients with cyclin D1-positive tumors as compared to patients with cyclin D1-negative tumors (adjusted hazard ratio for death [test set], 2.47, 95% confidence interval [1.08–5.63] P=0.03; adjusted hazard ratio for death [validation set], 1.91, [1.45–2.51] P<0.001). Relapse-free survival was also shorter in patients with cyclin D1-positive tumors than in patients with cyclin D1-negative tumors (adjusted hazard ratio for recurrence or death [test set], 2.73, [1.50–4.96] P=0.001; adjusted hazard ratio for recurrence or death [validation set], 1.60, [1.19–2.16] P=0.002). Conclusions: Women with early-stage, hormone receptor-positive breast cancer and cyclin D1-negative tumors benefit more from adjuvant tamoxifen therapy than women with cyclin D1-positive tumors. No significant financial relationships to disclose.