Thailand Medical Study Finds Tamoxifen Prevents Breast Cancer Return After Mastectomy
Nikhil Prasad Fact checked by:Thailand Medical News Team Feb 20, 2026 1 hour, 36 minutes ago
Thailand Medical: A new breast cancer study from researchers at the Faculty of Medicine Siriraj Hospital under Mahidol University has delivered important new evidence showing that tamoxifen, a well-known hormone therapy drug, can significantly reduce the risk of breast cancer returning even after complete breast removal surgery. The findings challenge the long-standing belief that mastectomy alone always eliminates future cancer risk in patients with ductal carcinoma in situ (DCIS).
Tamoxifen therapy significantly lowers breast cancer recurrence risk after full breast removal surgery
DCIS Patients Still Face Hidden Risk After Surgery
DCIS is an early form of breast cancer where abnormal cells remain inside the milk ducts and do not invade surrounding breast tissue. Because of its localized nature, many patients undergo mastectomy and are considered effectively cured. However, some patients later experience recurrence, either in the chest wall, the opposite breast, or in rare cases, distant organs.
Although DCIS generally has excellent survival rates, recurrence can be serious when it happens, particularly if it returns as invasive cancer. This makes long-term prevention strategies extremely important.
Major Differences Seen Between Patients Who Took Tamoxifen and Those Who Did Not
The research team analyzed 180 women with hormone receptor-positive DCIS who underwent mastectomy between 2008 and 2017. Of these patients, 120 received tamoxifen therapy after surgery, while 60 received no hormone therapy.
After more than eight years of follow-up, only 5 patients in the tamoxifen group experienced recurrence, compared to 11 patients in the non-tamoxifen group. This
Thailand Medical News report highlights a significant difference in long-term outcomes between the two groups.
The 10-year recurrence-free survival rate was 94.7 percent in patients who took tamoxifen, compared to 77.9 percent in those who did not receive the drug. Statistical analysis confirmed that tamoxifen reduced recurrence risk by more than 80 percent, demonstrating a strong protective effect.
Most Recurrences Occurred in Opposite Breast or Spread to Other Organs
Among the 16 patients who experienced recurrence, the majority developed cancer in the opposite breast. Two patients had recurrence in the chest wall, and three patients developed distant metastases involving organs such as the liver and bones. All patients with distant metastases died during follow-up, underscoring the seriousness of recurrence when it spreads beyond the breast.
Researchers also observed that recurrence typically occurred within the first several years after surgery, with most cases appearing within six years.
How Tamoxifen Helps Prevent Cancer from Returning
Tamoxifen works by blocking estrogen receptors in breast tissue. Many DCIS tumors depend on estrogen signals to grow. By preventing estrogen from activating these receptors, tamoxifen helps stop any r
emaining microscopic cancer cells from multiplying and forming new tumors.
Importantly, most patients in the tamoxifen group adhered well to treatment, with 78 percent completing the recommended five-year therapy course. Researchers also reported no serious side effects such as uterine cancer or blood clots during the study period, although careful monitoring remains necessary.
Important Implications for Future Breast Cancer Treatment
These findings suggest that tamoxifen provides valuable additional protection even in patients who have already undergone mastectomy. While mastectomy remains highly effective, this study shows that hormone therapy can further reduce the risk of recurrence and improve long-term outcomes.
The results may encourage physicians to consider tamoxifen more frequently for patients with hormone-sensitive DCIS, particularly those at higher risk of recurrence.
Conclusion
This important study demonstrates that tamoxifen offers significant protective benefits for women with hormone-sensitive DCIS who undergo mastectomy. By substantially lowering recurrence rates and improving long-term survival outcomes, tamoxifen provides an additional safeguard against future cancer development. These findings reinforce the importance of combining surgical treatment with carefully selected hormone therapy to maximize patient protection. Women diagnosed with DCIS should consult qualified medical professionals to determine whether tamoxifen therapy may offer meaningful additional benefit in their individual case.
The study findings were published in the peer reviewed journal: Current Oncology.
https://www.mdpi.com/1718-7729/33/2/89
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Medical News.
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https://www.thailandmedical.news/articles/cancer
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