This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record.
1. Trial at a Glance
DATA was a randomized phase 3 trial evaluating different durations of adjuvant anastrozole after 2 to 3 years of adjuvant tamoxifen in postmenopausal hormone-sensitive breast cancer patients. The primary endpoint was disease-free survival (DFS), assessed at different time frames corresponding to the assigned duration of anastrozole.
| Feature | DATA |
|---|---|
| Trial acronym | DATA |
| ClinicalTrials.gov identifier | NCT00301457 |
| Official title | Different Durations of Adjuvant Anastrozole Therapy After 2 to 3 Years Tamoxifen Therapy in Breast Cancer |
| Phase | Phase 3 |
| Status | Completed |
| Condition | Breast Cancer |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None |
| Primary purpose | Treatment |
| Enrollment | 1914 |
| Number of arms | 2 |
| Intervention | Anastrozole |
| Lead sponsor | Maastricht University Medical Center |
| Sponsor type | Other |
2. Clinical Question
The central question was whether extending adjuvant anastrozole therapy from 3 years to 6 years improves disease-free survival in postmenopausal hormone-sensitive breast cancer patients who had already received 2 to 3 years of adjuvant tamoxifen.
Population
Postmenopausal hormone-sensitive breast cancer patients subsequent to 2 to 3 years of adjuvant tamoxifen.
Intervention
6 years of adjuvant anastrozole subsequent to 2 to 3 years of adjuvant tamoxifen.
Comparator
3 years of adjuvant anastrozole subsequent to 2 to 3 years of adjuvant tamoxifen.
Primary question
Does 6 years of adjuvant anastrozole produce different disease-free survival from 3 years of adjuvant anastrozole after 2 to 3 years of tamoxifen?
3. Trial Design
6 years of adjuvant anastrozole
- Adjuvant anastrozole
- 6 years of anastrozole
- Administered subsequent to 2 to 3 years of adjuvant tamoxifen
3 years of adjuvant anastrozole
- Adjuvant anastrozole
- 3 years of anastrozole
- Administered subsequent to 2 to 3 years of adjuvant tamoxifen
4. Endpoints
The registry identifies one registered primary endpoint: disease-free survival with 6 years of adjuvant anastrozole compared with 3 years of adjuvant anastrozole after 2 to 3 years of adjuvant tamoxifen.
| Endpoint | Registry definition | Time frame |
|---|---|---|
| Primary: Disease-free survival | To assess the disease free survival (DFS) with 6 years of adjuvant anastrozole compared with 3 years of adjuvant anastrozole in postmenopausal hormone sensitive breast cancer patients, subsequent to 2 to 3 years of adjuvant tamoxifen | After 9 years for the group with 6 years of adjuvant anastrozol, subsequent to 2 to 3 years of adjuvant tamoxifen or after 6 years for the group with 3 years of adjuvant anastrozole subsequent to 2 to 3 years of adjuvant tamoxifen |
5. Statistical Structure of the Primary Endpoint
Disease-free survival is a time-to-event endpoint. Unlike a simple proportion measured at one fixed visit, a time-to-event analysis uses both whether an event occurs and the time at which it occurs. Patients who have not experienced the relevant event by the end of their available observation can contribute follow-up information through censoring.
Here, T represents the time to the event defining the disease-free survival endpoint. The survival function gives the probability of remaining event-free beyond time t.
The registry identifies the endpoint but does not post a formal statistical-analysis result or a detailed statistical-analysis plan in the information represented here. For a randomized comparison of disease-free survival, standard analyses would typically include Kaplan-Meier estimation of the disease-free survival function, a comparison of the randomized groups using a log-rank framework, and estimation of a hazard ratio using a Cox proportional-hazards model.
6. Planned Analysis
The registry says that the primary analysis will assess disease-free survival with 6 years of adjuvant anastrozole compared with 3 years of adjuvant anastrozole in postmenopausal hormone-sensitive breast cancer patients after 2 to 3 years of adjuvant tamoxifen.
| Statistical component | Typical approach for this endpoint | Purpose |
|---|---|---|
| Kaplan-Meier estimator | Estimate disease-free survival over time | Describe the event-free experience of each randomized group while accounting for censoring |
| Log-rank comparison | Compare survival distributions between randomized groups | Test whether the disease-free survival experience differs between treatment durations |
| Cox proportional-hazards model | Estimate a hazard ratio and confidence interval | Quantify the relative instantaneous event rate between the two randomized groups |
| Time-specific survival estimates | Estimate disease-free survival at clinically relevant times | Provide an absolute interpretation alongside any relative effect measure |
Why Kaplan-Meier analysis fits the endpoint
Patients in a disease-free survival analysis may be followed for different lengths of time. A Kaplan-Meier estimator uses the information available up to each patient's event or censoring time rather than requiring every patient to be observed for an identical duration. This is particularly important when the outcome is explicitly defined in terms of time until an event.
Why a hazard ratio can be useful
A hazard ratio summarizes the relative instantaneous event rate between randomized groups under a proportional-hazards model. A value below 1 would indicate a lower estimated event rate in the numerator group, whereas a value above 1 would indicate a higher estimated event rate. It is not itself a probability of remaining disease-free and is not the same as a difference in disease-free survival percentages.
7. Interpreting Disease-Free Survival in This Trial
The DATA trial is statistically interesting because the intervention is not a new drug versus placebo. Both randomized groups receive anastrozole; the experimental contrast is the duration of exposure to adjuvant anastrozole after an initial period of tamoxifen.
Duration is the treatment contrast
The randomized question is whether 6 years of anastrozole produces a different DFS experience from 3 years of anastrozole.
Prior therapy is common to the comparison
Both groups are described in the primary endpoint as receiving anastrozole subsequent to 2 to 3 years of adjuvant tamoxifen.
DFS is longitudinal
The primary outcome is defined over time rather than as a simple binary outcome at a single visit.
Follow-up is built into the endpoint
The registry specifies different assessment horizons corresponding to the assigned anastrozole duration.
This structure means that the statistical comparison should focus on the randomized treatment-duration contrast rather than simply comparing the number of patients who are disease-free at one arbitrary calendar date. Time-to-event methods preserve more of the information contained in the observed follow-up.
8. Statistical Methods Explained
What does disease-free survival mean statistically?
Disease-free survival is a time-to-event measure. The statistical object is the distribution of time until the event defining DFS, rather than only whether an event eventually occurred. This allows the analysis to incorporate both event timing and censored follow-up.
Why use a Kaplan-Meier estimator?
Kaplan-Meier estimation is designed for time-to-event data in which some observations may be censored. It estimates the probability of remaining event-free over time without requiring every patient to experience the event during observation.
Why would a log-rank test be appropriate?
A log-rank test provides a standard way to compare two randomized groups across their observed time-to-event distributions. It uses the ordering of events and the number of patients at risk at each event time rather than reducing the analysis to a single fixed-time proportion.
What does a hazard ratio tell us?
A hazard ratio compares estimated instantaneous event rates between groups under a proportional-hazards model. For example, an HR of 0.70 would correspond to a 30% lower estimated hazard in the treatment group relative to the comparator because 1 − 0.70 = 0.30. It would not mean that exactly 30% fewer patients experience the event or that every patient has a 30% reduction in individual risk.
Why is the proportional-hazards assumption important?
The Cox hazard ratio is most naturally interpreted as a common relative hazard over the period represented by the model. If the relative hazards change substantially over time, a single hazard ratio may compress a more complicated pattern into one number. Kaplan-Meier curves and time-specific disease-free survival estimates can provide additional context.
Why does randomization matter for the statistical comparison?
Randomization creates the treatment-duration comparison before outcomes are observed. With randomized allocation, the primary efficacy analysis can compare groups according to assigned treatment rather than allowing post-randomization treatment decisions to determine the main comparison.
9. Time Frame and Interpretation
Trial start
The registry lists June 2006 as the study start date.
Two anastrozole durations
The trial compares 6 years with 3 years of adjuvant anastrozole after 2 to 3 years of adjuvant tamoxifen.
Primary completion
The registry lists April 2022 as the primary completion date.
The primary endpoint's time-frame wording creates an important statistical distinction: the registry specifies 9 years for the group assigned to 6 years of adjuvant anastrozole and 6 years for the group assigned to 3 years of adjuvant anastrozole. These are the endpoint's stated assessment horizons and should not be silently replaced by a different follow-up convention.
10. Randomization and Open-Label Design
Randomization supports a direct comparison of the assigned treatment durations. The absence of masking means that treatment assignment was not blinded. For a disease-free survival endpoint, this distinction can matter when assessment of disease status involves clinical or diagnostic judgment. The registry information presented here does not specify an independent blinded endpoint-adjudication process.
11. What the Primary Endpoint Can Establish
A valid randomized comparison of DFS can address whether the disease-free survival experience differs between the two assigned durations of anastrozole. A hazard ratio, if reported from an appropriate model, would provide a relative measure of the event rate, while Kaplan-Meier estimates would describe the pattern of disease-free survival over time.
A hazard ratio is a relative measure. It describes the relationship between the estimated event hazards in the two randomized groups and should not be read as an absolute percentage-point difference in DFS.
Time-specific disease-free survival estimates would answer a different question: what proportion of patients remain disease-free at a specified time under each assigned duration? Absolute and relative measures are complementary rather than interchangeable.
A confidence interval around a hazard ratio would quantify statistical uncertainty around the estimated relative effect. A narrow interval indicates greater statistical precision than a wide interval, while the interval's position relative to the null value of 1 is relevant to conventional hypothesis testing.
If a p-value were reported, it would describe the compatibility of the observed data with the specified null hypothesis under the statistical model and testing framework. It would not measure the size or clinical importance of the treatment-duration effect.
12. Important Limitations and Interpretation Issues
- No posted statistical results: the ClinicalTrials.gov record does not report a hazard ratio, confidence interval, p-value, event count, or disease-free survival estimate for the registered primary endpoint.
- Open-label design: the registry identifies masking as none, so treatment assignment was not blinded.
- Limited endpoint detail: the registry defines the primary endpoint and its time frame but does not provide the detailed event definition, censoring rules, analysis population, or statistical-analysis plan in the information reported here.
- No subgroup results: the registry information does not provide subgroup-specific DFS estimates or treatment-effect estimates.
- No safety results: the registry information does not report serious adverse-event counts by randomized arm.
- No multiplicity framework reported: the registry information does not specify a multiplicity-adjustment procedure for the primary endpoint or other analyses.
- No interim-analysis framework reported: the registry information does not specify interim efficacy looks, alpha spending, stopping boundaries, or a group-sequential design.
- No missing-data or imputation framework reported: the registry information does not specify censoring rules, missing-data handling, or imputation procedures for the primary endpoint.
13. Why This Trial Matters Statistically
DATA is a useful statistical case study because it isolates a clinically important design question: does extending the duration of an existing adjuvant therapy change a time-to-event outcome? The comparison is not simply treatment versus no treatment. Both groups receive anastrozole, while the randomized distinction is the duration of therapy after prior tamoxifen.
| Concept | How it appears in DATA |
|---|---|
| Randomization | 1914 patients were enrolled in a randomized phase 3 trial. |
| Parallel design | The registry identifies 2 parallel arms. |
| Duration comparison | The primary question compares 6 years with 3 years of adjuvant anastrozole. |
| Prior therapy | The comparison follows 2 to 3 years of adjuvant tamoxifen. |
| Time-to-event analysis | The primary endpoint is disease-free survival. |
| Kaplan-Meier estimation | A standard approach for describing disease-free survival over time. |
| Hazard ratio | A standard relative measure for comparing time-to-event hazards between randomized groups. |
| Censoring | Time-to-event methods can retain follow-up information from patients whose event status is not observed through the full analysis period. |
| Open-label design | The registry identifies masking as none. |
| Follow-up horizon | The registry specifies 9 years for the 6-year group and 6 years for the 3-year group. |
14. The Statistical Question Behind Treatment Duration
Duration trials require a slightly different way of thinking about treatment effects. The scientific question is not simply whether anastrozole works. The randomized question is whether additional exposure to anastrozole changes the subsequent disease-free survival experience.
That distinction matters because the relevant contrast is defined by the two randomized strategies. A comparison of patients who happen to remain on treatment for different lengths of time would not have the same causal interpretation as the randomized comparison of assigned durations.
The exact statistical representation may be a difference in survival probabilities, a difference in restricted mean survival time, a hazard ratio, or another prespecified time-to-event estimand. The registry identifies DFS as the primary endpoint but does not report the formal estimand or statistical-analysis specification.
15. Primary Endpoint Assessment Horizon
6-year anastrozole group
The registered primary endpoint is assessed after 9 years for the group receiving 6 years of adjuvant anastrozole subsequent to 2 to 3 years of tamoxifen.
3-year anastrozole group
The registered primary endpoint is assessed after 6 years for the group receiving 3 years of adjuvant anastrozole subsequent to 2 to 3 years of tamoxifen.
The difference in stated assessment horizons reflects the different treatment durations. In interpreting the registry endpoint, it is therefore important to retain the time-frame wording rather than treating the comparison as an unspecified duration of follow-up.
16. Disease-Free Survival: A Practical Statistical Framework
Step 1: Define the time origin
A time-to-event analysis requires a clearly defined starting point. The registry defines the primary endpoint in relation to the treatment-duration comparison following 2 to 3 years of adjuvant tamoxifen. The detailed analysis record does not specify the exact statistical time origin used for an event-time calculation.
Step 2: Define the event
The registry names disease-free survival as the endpoint but does not provide the detailed component-event definition in the information reported here. The exact event definition is therefore an important part of any full statistical-analysis plan.
Step 3: Record follow-up and censoring
Each participant contributes observed time until the relevant event or censoring. Patients with incomplete event observation can still contribute information before censoring, provided the censoring assumptions required by the analysis are appropriate.
Step 4: Estimate the survival curves
Kaplan-Meier curves can display the estimated probability of remaining disease-free over time for each randomized group. The separation, timing, and shape of the curves can provide information that a single summary statistic cannot fully capture.
Step 5: Quantify the relative treatment effect
A Cox model can summarize the relative event hazard as a hazard ratio. The proportional-hazards assumption should be considered when interpreting a single HR over a long follow-up period.
17. Clinical Interpretation vs Statistical Interpretation
Statistical interpretation
The registered primary analysis asks whether disease-free survival differs between randomized 6-year and 3-year anastrozole strategies after 2 to 3 years of tamoxifen. Time-to-event methods are naturally suited to this endpoint.
Clinical interpretation
The clinical question concerns whether extending the duration of adjuvant anastrozole changes the period during which patients remain disease-free. The registry does not report the observed magnitude of that difference.
The distinction is important: statistical significance, if demonstrated, would address evidence against a specified null hypothesis, while clinical interpretation would require consideration of the magnitude, precision, duration, and practical meaning of any observed treatment effect.
18. Trial History
Study start
The ClinicalTrials.gov record lists June 2006 as the study start date.
Different durations of adjuvant anastrozole
The trial evaluates 6 years versus 3 years of adjuvant anastrozole after 2 to 3 years of adjuvant tamoxifen.
Primary completion
The ClinicalTrials.gov record lists April 2022 as the primary completion date.
19. What Would Make a Disease-Free Survival Result Informative?
A complete statistical interpretation of the primary endpoint would ideally bring several quantities together rather than relying on one number.
| Quantity | What it would contribute |
|---|---|
| Kaplan-Meier estimate | Shows the estimated probability of remaining disease-free over time. |
| Median DFS | Provides the time by which an estimated 50% of the relevant population has experienced the endpoint, when the median is estimable. |
| Hazard ratio | Provides a relative comparison of event hazards under a Cox-type model. |
| 95% confidence interval | Describes statistical uncertainty around the estimated treatment effect. |
| P-value | Assesses the data relative to the prespecified null hypothesis and testing framework. |
| Time-specific DFS | Provides an absolute clinical perspective at a defined follow-up time. |
The ClinicalTrials.gov record does not report these observed primary-endpoint results. The absence of a posted estimate means that the registry entry establishes the question and design, but not the numerical magnitude of the observed treatment-duration effect.
20. Why Hazard Ratios Should Not Stand Alone
Even when a hazard ratio is available, it should be interpreted alongside the underlying survival curves and absolute disease-free survival estimates. A hazard ratio summarizes a relative relationship across follow-up; it does not directly state how many additional patients remain disease-free at a clinically meaningful time.
A hazard ratio can indicate the direction and relative magnitude of a treatment effect, while a time-specific DFS estimate shows the corresponding absolute event-free probability. Both perspectives are useful because they answer different statistical questions.
A Cox hazard ratio is model-based. Its interpretation depends on the model specification and the proportional-hazards assumption. When hazards change relative to one another over time, additional summaries may be more informative.
Time-to-event estimates depend on how censoring is handled and on assumptions concerning the relationship between censoring and the event process. The registry information does not specify the detailed censoring rules for this trial.
21. Sources
- ClinicalTrials.gov: DATA, NCT00301457.
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Clinical trial analyses can be read alongside broader statistical methods and educational resources covering randomized designs, survival analysis, and treatment-effect estimation.
22. Record Summary
DATA is a randomized phase 3 trial of treatment duration in postmenopausal hormone-sensitive breast cancer. Its primary statistical question is whether 6 years of adjuvant anastrozole produces a different disease-free survival experience from 3 years of adjuvant anastrozole after 2 to 3 years of adjuvant tamoxifen. The trial enrolled 1914 patients, used a two-arm parallel design, and was unmasked. The registered primary endpoint is disease-free survival, with the registry specifying assessment after 9 years for the 6-year anastrozole group and after 6 years for the 3-year anastrozole group.
From a statistical perspective, the trial is a useful example of a randomized time-to-event comparison in which the treatment contrast is duration rather than drug versus placebo. Kaplan-Meier estimation, log-rank comparison, and Cox proportional-hazards modeling are natural analytical frameworks for such an endpoint, while interpretation should distinguish relative hazard from absolute disease-free survival and should account for censoring and model assumptions.