Tamoxifen for Prevention of Breast Cancer: Report of the National Surgical Adjuvant Breast and Bowel Project P-1 Study
- Study type
- Clinical trial
- Study name
- NSABP P-1
- Phase
- Phase 3
- Design
- Randomised placebo-controlled trial for the prevention of breast cancer
- Sample size
- 13,388 women
- Source
- JNCI: Journal of the National Cancer Institute · 1998
In plain words
In this large study, more than 13 thousand women with a higher than usual risk of breast cancer took tamoxifen tablets or a placebo (dummy tablet) for 5 years. Tamoxifen cut the risk of breast cancer roughly in half. On the other hand, the risk of cancer of the womb lining (endometrium), stroke and blood clots in the veins or lungs went up, and these side effects were seen mostly in women aged 50 and over. The decision to take this medicine should be made with your doctor, taking into account your personal risk and the possible side effects.
Key results
Treatment arms and regimens
Tamoxifen 20 mg daily for 5 years (6681 women).
Placebo for 5 years (6707 women).
Source of the regimen details: Abstract of the paper
Doses are given for the information of specialists, as in this study’s protocol, and are not a prescription. Every drug must be prescribed by the treating physician for the individual patient.
Study population
Women at increased risk of breast cancer because of one of three conditions: (1) age 60 or older, (2) age 35 to 59 with a predicted 5-year breast cancer risk of at least 1.66%, or (3) a history of lobular carcinoma in situ (LCIS). The Gail algorithm was used to estimate the probability (risk) of developing breast cancer over time.
Endpoints
Incidence of invasive and non-invasive breast cancer, incidence of oestrogen receptor-positive and -negative tumours, and adverse events including ischaemic heart disease, fractures, endometrial cancer, stroke, pulmonary embolism and deep vein thrombosis.
Safety and side effects
Tamoxifen did not change the annual rate of ischaemic heart disease, but a reduction in hip, wrist (Colles) and spine fractures was observed. The rate of endometrial cancer increased in the tamoxifen group (risk ratio 2.53; 95% CI: 1.35 to 4.97), predominantly in women aged 50 or older. All endometrial cancers in the tamoxifen group were stage I (localised disease) and no deaths from endometrial cancer occurred in this group. No liver cancer and no increase in colon, rectal, ovarian or other cancers was seen in the tamoxifen group. Rates of stroke, pulmonary embolism and deep vein thrombosis were higher in the tamoxifen group, and these events occurred more often in women aged 50 or older.
Clinical significance and place in guidelines
Based on the abstract, tamoxifen may be appropriate as a breast cancer preventive agent in many women at increased risk, taking into account adverse events such as endometrial cancer and thromboembolic events. The current status of guidelines and drug approvals for chemoprevention should be checked separately.
Limitations
The published abstract reports follow-up up to 69 months. Long-term effects of the drug on survival and adverse events at longer follow-up are not reported in this abstract. The increased risk of endometrial cancer and thromboembolic events should be considered in individual decision-making.
This summary was prepared by the editorial team from the published paper; the original paper is the final reference. Read the original abstract on PubMed.