Sae-sim N.Samarnthai N.Numprasit W.Mahidol University2026-03-032026-03-032026-02-01Current Oncology Vol.33 No.2 (2026)https://repository.li.mahidol.ac.th/handle/123456789/115511Background: 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.MedicineArticleSCOPUS10.3390/curroncol330200892-s2.0-10503110059217187729