Low-Dose Tamoxifen for Preventing Breast Cancer Recurrence: Groundbreaking 10-Year Follow-Up

Tamoxifen reduces breast cancer recurrence by 42%. Follow-up over 10 years showed lasting protection without an increase in serious adverse effects.

Why Is This Study Important?

The expansion of breast cancer screening has led to more frequent diagnosis of early lesions that have not yet become invasive, such as ductal carcinoma in situ (DCIS) or atypical ductal hyperplasia (ADH) . However, some women with these lesions are at risk of developing invasive breast cancer in later years. There is therefore a substantial need for highly effective preventive treatments with minimal side effects.

The Italy-based study, whose results were published in 2023 in JCO , was the TAM-01 trial. It addressed precisely this need by examining low-dose tamoxifen (5 mg/day) for its long-term protective effects in women with previous DCIS, ADH and LCIS. Data from 10 years of follow-up suggest that this simple intervention may have a much stronger effect than expected .

TAM-01 Study Design: Who Took Part and What Was Done?

• Number of participants: 500 women
• Diagnoses: 69% DCIS, 20% ADH, 11% LCIS (lobular carcinoma in situ)
• Average age: 54 ± 9 years
• Postmenopausal status: 58% of participants were postmenopausal
• Intervention: Low-dose tamoxifen, 5 mg daily, or placebo for 3 years after surgery
• Follow-up duration: Median 9.7 years (IQR: 8.3 – 10.9)

Participants were randomly assigned to two groups: one received low-dose tamoxifen, and the other received placebo . Radiotherapy was administered in some cases according to clinical need.

Main Findings: Tamoxifen Significantly Reduces Recurrence Risk

Over 10 years of follow-up, 66 breast cancer cases were identified:

• 25 cases in the tamoxifen group
• 41 cases in the placebo group

The corresponding annual rates were:

• Tamoxifen: 11.3 cases / 1000 person-years
• Placebo: 19.5 cases / 1000 person-years

Statistical analysis:

• Tamoxifen reduced the risk of developing breast cancer by 42%. HR (Hazard Ratio): 0.58 (95% confidence interval, 0.35 – 0.95)
• p-value: 0.03, statistically significant

Further Results: Contralateral Protection and Subgroup Differences

• Contralateral breast cancer: In the tamoxifen group: 6; in the placebo group: 16 cases
  • HR: 0.36 (p = 0.025) → 64% risk reduction
• DCIS subgroup: Recurrence risk decreased by 50% (HR: 0.50; p = 0.02)

Number needed to treat (NNT):

• To prevent 1 cancer event over 5 years: 22 people
• Over 10 years, the number falls to 14 people .

These findings show that the protective effect of tamoxifen provides an increasing benefit over time.

Side Effects: Low Dose, Low Risk

Side effects are, of course, a major concern. However, the study found no increase in serious adverse effects even during 7 years of follow-up after 3 years of treatment . Low-dose tamoxifen does not carry the risks associated with the conventional 20 mg dose, such as hot flashes and thromboembolic events.

Conclusion: Low-Dose Tamoxifen Provides Strong Protection for Low-Risk Women

The most important message of this study is: Low-dose tamoxifen substantially reduces long-term ipsilateral (same breast) and contralateral (opposite breast) cancer recurrence in women with previous noninvasive breast lesions. Moreover, this protective effect continues for at least 7 years after treatment is stopped.

Clinical Implications: For Whom and When?

These results are particularly promising for postmenopausal women diagnosed with DCIS or ADH who have a moderate risk of invasive cancer . For patients concerned about side effects, the low-dose regimen may be a noteworthy option because it offers a balance of high efficacy and few side effects .