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NSABP P-1 (Breast Cancer Prevention Trial): What the Breast cancer Trial Found
NSABP P-1 (Breast Cancer Prevention Trial) tested tamoxifen vs placebo in breast cancer, measuring breast-cancer incidence. Plain-language summary of a result widely described as practice-influencing — and what it doesn't mean.
Original commentary from the Cancer Explained editorial team.
Historical context: this page explains an event dated 1998. It was published as an explainer on July 12, 2026 and is not breaking news.
Please note: this page is educational only — it is not medical advice, and it does not speculate about anyone’s health beyond reliable public reporting. For questions about your own health, talk with your healthcare team.
In brief
NSABP P-1 (Breast Cancer Prevention Trial) was randomized prevention trial in breast cancer that compared tamoxifen vs placebo and measured breast-cancer incidence. It reported a result widely described as practice-influencing.
Trial at a glance
| Field | Detail |
|---|---|
| Trial | NSABP P-1 (Breast Cancer Prevention Trial) |
| Identifier | Not recorded here |
| Phase | See report |
| Design | randomized prevention trial |
| Cancer type | Breast cancer |
| Comparator | tamoxifen vs placebo |
| Primary endpoint | breast-cancer incidence |
| Reported result | A result widely described as practice-influencing |
Who took part
The trial enrolled the population described in its report for breast cancer.
The main result
The trial's main finding concerned breast-cancer incidence: NSABP P-1 (Breast Cancer Prevention Trial) reported a result widely described as practice-influencing. Full numbers, follow-up, and statistical detail are held for verification against the peer-reviewed report or trial registry.
What the result means
Results like this help shape research and, sometimes, care — but a trial's finding is one piece of evidence, tied to the specific people and design it used.
What this does not mean
- A positive trial does not automatically mean a treatment is approved or available; approval and access are separate steps.
- Improvement on one measure does not always translate into every outcome that matters to patients.
- Trial participants are selected by specific criteria, so results may not apply to everyone with this cancer.
Questions you might bring to a clinician
- Does this apply to my specific cancer type and situation?
- Is this treatment approved and available, or still investigational?
- What are the main side effects, and how would they be managed?
Sources
This article was written from the sources below, which were checked on the source-check date shown above.
How this article was prepared
Prepared by Cancer Explained's AI-assisted editorial system and checked against the sources listed below. This article has not been reviewed by a healthcare professional unless a named reviewer is specifically shown.
Cancer Explained is published by the National Cancer Information Foundation as a nonprofit-oriented public-interest education project. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.
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