Benefit of low dose tamoxifen in a large observational cohort of high risk ER positive breast DCIS

Abstract

Low-dose tamoxifen has comparable antiproliferative effect to the standard dose of 20 mg/day in biomarker trials, but its clinical efficacy remains unclear. We assessed the effect of low-dose tamoxifen on ipsilateral recurrence in ductal carcinoma in situ (DCIS) patients treated in a referral Institution between 1996 and 2008. Following conserving surgery, women received radiotherapy and/or low-dose tamoxifen upon clinical judgment and patient preferences. Cox regression analyses were used with and without confounding factors. Among 1,091 women with DCIS and median age 53 years (IQR 46-62), 544 (49.9%) received radiotherapy. Of the 833 women with oestrogen receptor (ER) positive DCIS, 467 (56.1%) received low-dose tamoxifen. After a median of 7.7 years, 235 ipsilateral recurrences and 62 contralateral breast tumors were observed. Low-dose tamoxifen significantly decreased any breast event (HR=0.70, 95% CI, 0.54-0.91) and ipsilateral DCIS recurrence (HR=0.66, 95% CI, 0.49-0.88), but not ipsilateral invasive recurrence or contralateral tumors. Radiotherapy showed a large significant reduction for any breast event (HR=0.55, 95% CI, 0.42-0.72). Tamoxifen was more effective on all breast events in women aged >50 years than in women aged ≤50 (HR=0.51, 95% CI, 0.33-0.77 versus HR=0.84, 95% CI, 0.60-1.18, p-interaction=0.03). Age ≤50 years, positive margins, high Ki67, high grade and low BMI were independent predictors of ipsilateral recurrence. No increase of endometrial cancers and fewer deaths (P=0.015) were observed on tamoxifen.

Low-dose tamoxifen seems to be safe and effective in reducing ipsilateral recurrence in ER positive DCIS in women aged >50 years. A randomized trial is underway to confirm these findings. This article is protected by copyright. All rights reserved.

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