Extended adjuvant treatment with anastrozole: Results from the Austrian Breast and Colorectal Cancer Study Group Trial 6a (ABCSG-6a)

Abstract

527 Background: ABCSG Trial 6 demonstrated that postmenopausal women with pT1–3a, any N, M0 hormone receptor-positive early stage breast cancer (EBC) randomized to 2 years tamoxifen (TAM) in combination with aminoglutethimide (AG) 500 mg, followed by 3 years TAM (n=996), did not have an improved prognosis, when compared with patients treated with 5 years TAM (n=990). We present results from ABCSG-6a, an extended adjuvant trial of ABCSG-6, which investigates whether continuing treatment with anastrozole (‘Arimidex’) [ANA] will improve overall prognosis. Methods: Postmenopausal women who had received TAM in combination with AG (n=406), or TAM alone (n=450), were re-randomized to switch to ANA 1 mg/day or no treatment (NT) for a further 3 years. The primary endpoint was event-free survival. Local or regional relapse was confirmed histologically where possible. Differences between the treatment groups were assessed by log-rank test. Results: Tumors <1cm,1–2 cm, or > 2cm in diameter were found in 135, 402 and 319 patients, respectively. Of the 856 patients, 578 had N0 disease, 261 patients had 1–3 nodes and 17 patients had >4 nodes involved. 171 patients had a histological Grade 3 lesion and 685 patients had Grade 1, 2 or lobular carcinomas. At 5 years’ median follow-up, 86 patients experienced local regional, distant metastases or contralateral breast cancer. Significantly fewer patients in the ANA group experienced disease recurrence compared with the NT group (30 vs 56 patients, respectively; hazard ratio 0.64; 95% confidence interval 0.41, 0.99; p=0.047). There was no statistically significant difference with respect to overall survival. Conclusions: Significantly fewer patients receiving ANA experienced disease relapse compared with placebo following 5 years of TAM with or without AG in postmenopausal women with EBC. Our results show that postmenopausal women who have completed 5 years of therapy with TAM with or without AG benefit from extended adjuvant therapy with ANA. No significant financial relationships to disclose.