Journal of Clinical Oncology, 2004 ASCO Annual Meeting Proceedings (Post-Meeting Edition).
Vol 22, No 14S (July 15 Supplement), 2004: 532
© 2004 American Society of Clinical Oncology

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Abstract

Randomized comparison of adjuvant tamoxifen (Tam) versus no hormonal treatment for premenopausal women with node-positive (N+), early stage breast cancer: first results of International Breast Cancer Study Group Trial 13–93

International Breast Cancer Study Group (IBCSG), Bern, Switzerland

532

Background: The value of 5 years of Tam in premenopausal women with breast cancer and its benefit according to endocrine responsiveness of the tumor has not been completely defined. Methods: Between 1993 and 1999, IBCSG Trial 13–93 enrolled 1246 (planned sample size, 1225) premenopausal women with N+, early stage breast cancer. All patients (pts) received chemotherapy (ACx4 cycles followed by immediate or delayed classical CMFx3 cycles) to be followed by Tam (20 mg daily) for 5 years or no hormonal therapy. The primary endpoint was disease-free survival (DFS). Estrogen receptor (ER) content was determined locally by immunohistochemistry (IHC) for 56% of pts and ligand-binding assay (LBA) for 44%. Tumors were classified as ER-absent if IHC expression=none or LBA=0 fmol/mg cytosol protein; ER-low if IHC=negative or borderline or LBA=1–9 fmol/mg cytosol protein; and ER-positive otherwise. Results: 735 (59%) pts had ER-positive disease. 61% had 1–3 N+, 42% had tumors 2 cm, 11% had grade 1 and 40% had grade 2 tumors, and the median age was 44 years. Tam provided significantly longer DFS compared with no Tam for the pts with ER-positive tumors. Pts with ER-low tumors obtained an intermediate benefit from Tam and pts with ER-absent tumors may have experienced a detrimental effect of Tam. The test for trend was significant (p=0.002). Conclusions: Tam significantly improved prognosis in premenopausal patients with endocrine responsive disease. It should not be considered as adjuvant therapy in patients with ER-absent tumors.

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Abstract presentation from the 2004 ASCO Annual Meeting