# Tamoxifen Reduces Breast Cancer Recurrence in Women with DCIS Who Underwent Mastectomy

## TL;DR

Tamoxifen helps reduce breast cancer recurrence in women who had mastectomy for a specific type of early-stage breast cancer.

## Contribution

This study shows that tamoxifen reduces recurrence risk in ER-positive DCIS patients after mastectomy, a previously uncertain scenario.

## Key findings

- Tamoxifen users had a 94.7% 10-year recurrence-free survival rate compared to 68.7% in non-users.
- Recurrence was significantly lower in tamoxifen-treated patients (HR = 0.178; p = 0.001).

## Abstract

This retrospective cohort study evaluated the impact of adjuvant endocrine therapy on recurrence risk in patients with estrogen receptor (ER)-positive ductal carcinoma in situ (DCIS) treated with mastectomy. While tamoxifen is known to reduce subsequent breast cancer in patients with ER-positive DCIS undergoing breast-conserving surgery with radiation, its benefit after mastectomy remains uncertain. Among 180 patients with hormone-receptor-positive DCIS, those who received adjuvant tamoxifen had a significantly higher 10-year recurrence-free survival (RFS) rate than those who did not receive endocrine therapy (94.7% vs. 68.7%). These findings suggest that adjuvant tamoxifen provides a meaningful reduction in recurrence risk and improves long-term outcomes in patients with ER-positive DCIS after mastectomy.

Background: Adjuvant tamoxifen reduces recurrence in patients with ER-positive DCIS treated with lumpectomy and radiation, but its benefit after mastectomy remains unclear. Methods: We retrospectively analyzed 287 patients who underwent mastectomy for pure DCIS at Siriraj Hospital between 2008 and 2017. Recurrence risk factors were assessed using log-rank test, and survival probabilities were estimated with Kaplan–Meier analysis. Results: Of 180 patients with hormone receptor (HR)-positive pure DCIS treated with mastectomy, 120 (66.7%) received tamoxifen, while the remaining 60 (33.3%) did not. The median follow-up was 8.07 years (0.05–13.8 years). Sixteen (8.9%) recurrences were identified, with 5 in the tamoxifen group and 11 in non-endocrine-therapy (ET) group. The 10-year recurrence-free survival (RFS) was 94.7% in the tamoxifen group compared with 77.9% in the non-ET group. Patients with HR-positive DCIS treated with tamoxifen following mastectomy had significantly less subsequent breast cancer (HR = 0.178; p = 0.001). Conclusions: Recurrence of breast cancer after mastectomy for DCIS is rare; however, it carries a high mortality rate for those who relapse. Adjuvant tamoxifen after mastectomy demonstrated a significant reduction in the risk of recurrence in ER-positive DCIS. This study supports the decision to prescribe adjuvant ET in patients with DCIS who underwent mastectomy.