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ATAC: What the Breast cancer Trial Found
ATAC tested anastrozole vs tamoxifen in breast cancer, measuring disease-free survival. 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 2005. 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
ATAC was phase 3, randomized, double-blind in breast cancer that compared anastrozole vs tamoxifen and measured disease-free survival. It reported a result widely described as practice-influencing.
Trial at a glance
| Field | Detail |
|---|---|
| Trial | ATAC |
| Identifier | Not recorded here |
| Phase | Phase 3 |
| Design | phase 3, randomized, double-blind |
| Cancer type | Breast cancer |
| Comparator | anastrozole vs tamoxifen |
| Primary endpoint | disease-free survival |
| 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 disease-free survival: ATAC 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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