Journal of Clinical Oncology, 2008 ASCO Annual Meeting Proceedings (Post-Meeting Edition).
Vol 26, No 15S (May 20 Supplement), 2008: 513
© 2008 American Society of Clinical Oncology

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Abstract

aTTom (adjuvant Tamoxifen—To offer more?): Randomized trial of 10 versus 5 years of adjuvant tamoxifen among 6,934 women with estrogen receptor-positive (ER+) or ER untested breast cancer—Preliminary results

University of Birmingham, Birmingham, United Kingdom; University of Warwick, Coventry, United Kingdom; University of Cambridge, Cambridge, United Kingdom; Worthing Hospital, Worthing, United Kingdom; University Hospital Coventry, Coventry, United Kingdom

513

Background: In ER+ early breast cancer, 5 years of tamoxifen substantially reduces the annual recurrence rate throughout the first decade (years 0–9). Despite this, appreciable risks of recurrence remain, with similar annual recurrence risks for ER+ disease during years 0–4, 5–9 and 10–14 following surgery. It is not reliably known how 10 years duration of adjuvant tamoxifen compares with the current standard of 5 years. Methods: Between 1991 and 2005, 6,934 women with ER+ (39%), or ER untested (61%) invasive breast cancer (53% node negative, 31% node positive, 16% node status unspecified) from 176 UK centers, who had completed 4+ years of adjuvant tamoxifen, were randomized between continuing for another 5 years and stopping. Information on compliance, hospital admission(s), breast cancer recurrence (including new contralateral disease), other new primary cancer, death and cause of death was sought annually. Results: 78% of those allocated to continue and 3% of those allocated to stop were taking adjuvant tamoxifen at 3 years following randomization; fewer than 1% switched to any other adjuvant hormone treatment. With a median follow-up of 4.2 years, there were fewer recurrences (415 vs 442; RR=0.94, 95% CI 0.81–1.09; p=0.4) among those allocated to 10yrs than 5yrs tamoxifen. Although breast cancer mortality was lower among those allocated 10yrs, with just 374 deaths from breast cancer recorded, data remain immature. Despite a doubling in the risk of endometrial cancer (76 vs 35) with 10yrs tamoxifen, there was no increase in deaths from endometrial cancer (10 vs 12) or from any other non-breast cancer cause. Conclusions: Although no significant reduction in recurrence has yet been seen in aTTom, the results are consistent with preliminary findings from the ATLAS trial, which reported a DFS but not overall survival advantage to longer tamoxifen (Peto et al SABCS 2007). Combining results from these two large studies indicate that continuation of tamoxifen beyond the first 5 years reduces recurrence over the next few years, but further follow-up is needed to assess reliably the longer-term effects on recurrence and the net effects, if any, on mortality.

No significant financial relationships to disclose.

Abstract presentation from the 2008 ASCO Annual Meeting