Safety/Efficacy of Letrozole Monotherapy or in Combination With Zoledronic Acid as Extended Adjuvant Treatment of Postmenopausal Patients With Primary Breast Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety/Efficacy of Letrozole Monotherapy or in Combination With Zoledronic Acid as Extended Adjuvant Treatment of Postmenopausal Patients With Primary Breast Cancer (NCT00332709), a randomized phase 3 study. The primary outcome is Change in Bone Mineral Density (BMD) From Baseline to Month 36.

2. Clinical Question

The clinical question focuses on bone mineral density during extended adjuvant treatment in a specific postmenopausal breast cancer population. The registry describes a prospective, randomized, two-arm comparison of letrozole alone with letrozole plus zoledronic acid. It identifies the primary measure as the percent change in lumbar-spine bone mineral density, measured by dual X-ray absorptiometry, from baseline to month 36.

The comparison addresses whether the recorded average change in this measure differed between the assigned groups. The posted primary results include participants with observations at both baseline and endpoint. The reported group sizes are therefore endpoint-analysis counts, and should not be assumed to represent every person enrolled or randomized. Details of treatment adherence, discontinuations, and reasons for missing endpoint measurements are not reported in the registry record.

3. Trial Design

The registry describes a prospective, randomized, open-label, parallel-group phase III trial. Participants were assigned to letrozole alone or to letrozole combined with zoledronic acid. Masking is recorded as none, so the trial was open-label. The registry reports enrollment of 83 and a completed status. The recorded start was 2006-01 and primary completion was 2010-08. The trial did not recruit patients in the United States.

The population was postmenopausal patients with operable breast cancer who had completed 4 to 6 years of adjuvant tamoxifen therapy after resection of the tumor. Both groups received letrozole orally at 2.5 mg per day for 3 years. The combination group also received zoledronic acid 4 mg by infusion every 6 months. The registry identifies osteoporosis and postmenopausal status among the listed conditions.

Bone mineral density change from baseline to month 36 was the primary outcome. The endpoint description specifies lumbar spine L1-L4, measurement by dual X-ray absorptiometry, and change expressed as a percent of baseline. The primary analysis included participants with observations at both baseline and endpoint. The recorded arm sizes for this outcome are 21 for letrozole and 20 for the combination group.

Secondary outcomes listed in the record include bone mineral density change at 12 months, fracture counts by visit, median disease-free survival, and changes in T-score and Z-score at month 12. Numerical results are available for some, but not all, of these measures. The randomization procedure, allocation concealment, protocol-specific analysis plan, original sample-size justification, and details of treatment compliance are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Total Randomized participants were 83. 2 patients were enrolled but never received study medication. Hence, 81 were included in the safety population.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: (ITT) The study population will consist of post menopausal breast cancer patients who have completed 4 to 6 years of adjuvant Tamoxifen therapy after therapy. Participants with observations at both baseline and endpoint were included in the analysis.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change in Bone Mineral Density (BMD) From Baseline to Month 36, measured over at 36 months as compared to baseline.

The primary endpoint is the percent change in lumbar-spine bone mineral density from baseline to month 36. Bone mineral density was measured by dual X-ray absorptiometry in the lumbar spine, specified as L1-L4. The registry defines the calculation as the month 36 measurement minus the baseline measurement, divided by the baseline measurement, then multiplied by 100. The unit is percent, and the recorded summary is a mean with standard deviation.

This endpoint describes average change in a continuous measurement of bone density over the stated follow-up period. In general, a continuous endpoint retains information about the magnitude of measurements rather than reducing them to categories. A baseline-referenced change score also expresses each participant’s later measurement relative to that participant’s starting measurement. These are general reasons such measures may be used in clinical research; the record does not provide a separate rationale for selecting this particular endpoint.

The endpoint is a measurement outcome, not a direct account of fractures or disease-free survival. Those measures appear among the listed secondary outcomes. The primary analysis population is described as intention-to-treat, but the record also specifies that participants needed observations at both baseline and endpoint to be included. The resulting reported group sizes are 21 and 20. How participants without both measurements were handled beyond this stated inclusion rule is not reported in the registry record.

7. Results Posted in the Registry

• Letrozole + Zoledronic Acid: mean 0.03 versus -0.11 on control; difference 0.14 (95% CI 0.07 to 0.21), standardized effect d = 1.22; z-test p = <0.001.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Change in Bone Mineral Density From Baseline to 12 Months

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Letrozole + Zoledronic Acid: mean 0.02 versus -0.04 on control; difference 0.06 (95% CI 0.03 to 0.09), standardized effect d = 1.33; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Letrozole + Zoledronic Acid than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change in T-Score From Baseline to Month 12

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Letrozole + Zoledronic Acid: mean 0.25 versus -0.31 on control; difference 0.56 (95% CI 0.36 to 0.76), standardized effect d = 1.62; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Letrozole + Zoledronic Acid than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change in Z-Score From Baseline to Month 12

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Letrozole + Zoledronic Acid: mean 0.37 versus -0.26 on control; difference 0.63 (95% CI 0.42 to 0.84), standardized effect d = 1.73; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Letrozole + Zoledronic Acid than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The posted numerical secondary results follow a broadly consistent direction across the three bone measures with numerical estimates. At month 12, the average bone mineral density change, T-score change, and Z-score change are each higher in the combination group than in the letrozole-only group. Their unadjusted comparisons have p-values of <0.001. These outcomes offer related measurements of bone status at an earlier time point; they are not independent replications of the month 36 primary endpoint.

These secondary findings complement the primary result because they concern bone-related measures and point in the same direction in this record. They do not replace the primary comparison, which is defined at month 36 and focuses on lumbar-spine bone mineral density. The secondary measures have different scales and timeframes, and should not be pooled conceptually as though they measured an identical outcome. The record also lists fracture counts by visit and median disease-free survival, but numerical results for those listed outcomes are not reported in the registry record.

Unadjusted secondary p-values carry less weight when multiple outcomes and time points are examined. General statistical explanation: as the number of statistical tests increases, the chance of at least one small p-value arising by chance can increase if no multiplicity strategy is used. The registry record does not report a multiplicity adjustment or a prespecified hierarchy for interpreting secondary outcomes. The secondary comparisons are therefore best treated as supportive, descriptive evidence rather than stand-alone confirmatory tests.

There are also differences in the numbers analyzed across the secondary measures. The record does not explain those differences or give a full account of missing observations. Because the measures are related and the analysis counts are not identical, the pattern should be interpreted as a set of posted group summaries, not as a complete account of all participants’ responses or all outcomes considered during the trial.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Change in Bone Mineral Density From Baseline to 12 Months
• Number of Participants With Any Kind of Fractures, by Visit.
• Median Disease Free Survival (DFS)
• Change in T-Score From Baseline to Month 12
• Change in Z-Score From Baseline to Month 12

9. Statistical Interpretation

10. Statistical Methods Explained

What does a mean change represent?

The endpoint is continuous and summarized by a mean. A mean is the arithmetic average of the recorded changes among participants included in an arm’s endpoint analysis. The registry also posts a standard deviation, which describes the spread of individual measurements around their group mean. General statistical interpretation: a mean gives a concise description of the group’s average, while the standard deviation gives information about variability between participants. Neither measure alone describes every participant’s outcome.

The endpoint is defined as percent change from baseline rather than the absolute bone mineral density value at month 36. The reported group mean therefore summarizes relative change using the registry’s stated calculation. It is important to keep the unit in view: the difference of 0.14 is a difference in percentage-point change, not a 14 percent difference in the groups’ measurements.

How is the group contrast formed?

The contrast compares the combination group’s mean with the letrozole group’s mean. In plain language, it is the average change in the combination group minus the average change in the letrozole-only group. The posted group means are 0.03 and -0.11 percent, respectively, and the posted mean difference is 0.14. This is an unadjusted comparison based on the group summaries. It does not incorporate a regression adjustment or a correction for other measured characteristics, because no such analysis is reported in the registry record.

Random assignment can support a fair comparison by balancing measured and unmeasured participant characteristics on average across groups, but randomization does not guarantee exact balance in a particular trial. The record states that allocation was randomized, but details of the randomization and allocation process are not reported. The open-label design means masking was absent; the record does not describe whether knowledge of assignment affected measurement procedures or follow-up.

What does the p-value say?

The unadjusted p-value is <0.001. General statistical explanation: a p-value describes how unusual data at least as discrepant as those observed would be under a specified model in which the groups have no true mean difference. It is not the probability that the null model is correct. It also does not measure clinical importance, the probability that a result will replicate, or the chance that an individual participant will experience a particular outcome.

The comparison is calculated from posted summary statistics, rather than reported as a separate registry analysis. It is therefore best understood as a simple unadjusted recalculation of the displayed group-level data. The registry record reports zero analyses and does not provide an adjusted primary analysis or a description of the trial’s statistical model. The posted p-value should not be interpreted as evidence that all relevant design or missing-data issues were addressed.

Why does variability matter?

Participants’ measurements can vary even when they receive the same assigned treatment. The standard deviations describe that observed spread in each group. General statistical explanation: variability affects how precisely a group mean and the between-group contrast can be estimated. Greater spread typically makes a fixed difference harder to distinguish from sampling fluctuation, while less spread can permit a more precise estimate. This relationship depends on sample size and the analysis assumptions as well as on the observed spread.

For the primary outcome, the posted standard deviations are 0.14 and 0.08 percentage points in the two groups. The summary data are treated as an ordinary continuous-outcome comparison. The registry does not report checks of distributional assumptions, a robust analysis, or a method for handling outliers. No conclusion about those aspects of the original analysis can be drawn from the record.

What does unadjusted mean?

An unadjusted group comparison uses the posted group summaries without incorporating other variables into a model. It is straightforward to interpret, but it may not match the trial sponsor’s planned analysis, if that analysis involved additional adjustments or design features. The record does not report the original statistical analysis plan, so the degree of correspondence between this recalculation and the planned primary analysis is not known. The discrepancy indicator is false, so the recalculated result does not conflict with a separately posted sponsor result; no separate sponsor comparison is listed.

General statistical explanation: an analysis plan can specify how to use baseline measurements, account for stratification, handle missing outcomes, and control the interpretation of multiple endpoints. These choices can affect standard errors, confidence intervals, and p-values. The registry record does not describe those methods for the primary result. The posted data therefore support interpretation of the simple summary-statistic contrast, rather than claims about an unreported model.

What does the analysis population label mean?

The primary population is labeled intention-to-treat, but the endpoint description states that participants with observations at both baseline and endpoint were included. The available wording does not establish how all randomized participants were handled in the analysis. General statistical explanation: intention-to-treat commonly refers to analyzing participants according to assigned group, while endpoint availability can create a distinction between the randomized population and the subset with usable measurements. The record does not report imputation, sensitivity analyses, or a detailed accounting of missing observations, so the label should be read together with the endpoint inclusion statement.

The arm counts for this outcome are 21 and 20. These are the posted analysis counts, not the trial’s enrollment count. Without a participant flow account, it is not possible to establish from the registry record why the endpoint counts differ from overall enrollment or whether missingness differed in meaningful ways across assigned groups.

11. Confidence Intervals and Precision

The confidence interval for the primary mean difference is 0.071 to 0.209 percentage points. The interval is centered around the posted difference of 0.14 and describes statistical uncertainty in the unadjusted estimate under the calculation’s assumptions. It is expressed on the same scale as the contrast: percentage-point difference in mean percent change in bone mineral density.

General statistical explanation: a confidence interval is a range of estimates compatible with the observed data under a specified method. It is not a guarantee that the true value lies in the interval, nor does it include every source of uncertainty. In particular, this interval does not capture uncertainties from unreported choices about missing data, outcome selection, or the trial’s original analysis plan. Those details are not reported in the registry record.

The interval lies above zero, which is consistent with the unadjusted p-value of <0.001 for a test of no mean difference. This agreement reflects related ways of expressing the same statistical comparison; it is not independent confirmation. The interval quantifies precision for the mean contrast, not the range of individual participants’ changes. Individual outcomes may vary more widely than the uncertainty around the group mean difference.

The primary endpoint counts are 21 and 20. Smaller analysis groups generally yield less precise estimates than larger groups, all else equal. The recorded standard deviations also reflect the observed variation in each group. The confidence interval should therefore be read as precision for this particular summary-data comparison, not as a guarantee of precision in other populations or future studies.

The record does not report a clinically important difference threshold. Statistical precision alone cannot determine whether the interval’s values are clinically consequential. That judgment would require clinical context and evidence not included in the registry record.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations based on the observed primary effect, rather than the original trial’s design calculation. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The target effect is set to the stated fraction of the observed effect. The trial’s own original sample-size assumptions and justification are not reported in the registry record.

For planning at 100% of the observed effect, the figures are 11 participants per arm for 80% power and 15 participants per arm for 90% power. At 75% of the observed effect, they are 19 participants per arm for 80% power and 26 participants per arm for 90% power. At 50% of the observed effect, they are 43 participants per arm for 80% power and 57 participants per arm for 90% power.

In plain language, 80% power means that, if the assumed effect and planning assumptions were true, a study of that planned size would have an 80% chance of detecting a difference at the stated significance level. The 90% column expresses the corresponding chance using a higher target for detection. Smaller effects are harder to distinguish from random variation, so planning for a smaller effect requires more participants per arm. The figures are planning illustrations, not observed power for this completed trial.

These calculations use the observed effect as a starting point, and observed effects from small samples can be uncertain. The figures therefore should not be treated as a definitive recommendation for a future study. Planning would also require decisions about the target effect, outcome definition, analysis method, expected missing data, and other design features, none of which can be inferred from these illustrations alone.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.140; pooled standard deviation σ = 0.115.
2. n = 2 × (1.96 + 0.842)² × 0.115² / 0.140² = 10.5, rounded up to 11 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 0.14                      # observed difference in means
sigma <- 0.114757268916748                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(332709)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 11 (80% power), 15 (90% power)
 75% of observed effect: n per arm = 19 (80% power), 26 (90% power)
 50% of observed effect: n per arm = 43 (80% power), 57 (90% power)
power.t.test: 11.6 
Simulated power at n = 11 per arm: 0.781 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry record does not report a statistical plan for multiplicity, including whether the primary and secondary outcomes were arranged in a testing hierarchy or whether any adjustment was applied. It lists multiple secondary measures, including bone mineral density, fracture counts, disease-free survival, and T-score and Z-score changes. General statistical explanation: interpreting many outcomes or time points as separate confirmatory tests can increase the chance of false-positive findings unless the testing strategy is addressed. Without a reported strategy, the secondary p-values should be interpreted cautiously and should not be treated as if each were the sole planned test.

The record reports zero analyses and does not include a sponsor-reported analysis for the posted comparisons. It does not specify the primary endpoint model, whether baseline values were included as covariates, or whether any stratification factors were used. Details of interim analyses, stopping rules, and changes to the analysis plan are not reported in the registry record. No assumptions about those features can be made from the available results.

The primary outcome population is labeled intention-to-treat, with the qualification that participants with observations at both baseline and endpoint were included. The primary outcome counts are 21 and 20, while the trial enrollment is 83. The record does not provide a flow of participants by assigned group, reasons for missing endpoint data, or information on whether missingness was related to treatment or outcome. It also does not report imputation methods or sensitivity analyses for missing values.

Those omissions matter because analysis restricted to participants with both measurements may differ from an analysis of all randomized participants, particularly if endpoint availability is related to participants’ characteristics or outcomes. General statistical explanation: the direction and size of any resulting bias cannot be determined merely from the count of analyzed participants. The registry record does not provide enough information to assess that possibility. Similarly, details of adherence and treatment discontinuation are not reported, limiting interpretation of how closely assigned treatment reflects treatment actually received.

15. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: vertigo positional (2.5%), concomitant disease progression (2.5%), cholecystitis (2.5%), fall (2.5%), lower limb fracture (2.5%).

The registry lists serious adverse events among 40 participants at risk in the letrozole group and 41 in the combination group. Six participants in the letrozole group and 7 in the combination group are recorded as affected. Other adverse events are listed for 35 participants in each group, with at-risk counts of 40 and 41, respectively. These are registry counts; the record does not provide further detail about event duration, severity grading beyond the serious-event category, relationship to treatment, or how events were collected.

The listed serious-event terms each have a reported percentage of 2.5%: positional vertigo, concomitant disease progression, cholecystitis, fall, lower limb fracture, and axillary mass. The registry record does not specify in this listing whether these terms represent unique participants or how the percentage denominator was defined. The terms should therefore be read as reported event categories, not added together to produce a participant count.

Deaths are not reported in the registry record. These summaries do not establish that events were caused by a study treatment, and the counts alone do not provide a comparative safety analysis. The record does not describe statistical testing for adverse events or provide enough detail to assess rare events.

16. What the Result Does, and Does Not, Mean

The posted primary result describes an average difference in lumbar-spine bone mineral density change between the two assigned groups among participants with measurements at baseline and month 36. The combination group’s mean change was higher than the letrozole-only group’s mean change, and the unadjusted interval excludes zero. This is the statistical result for the endpoint and analysis counts recorded in the registry.

It does not directly establish what happened to every participant. Group averages can conceal a range of individual changes, and the posted standard deviations indicate that participants’ measurements varied within each group. The confidence interval concerns uncertainty in the group mean difference, not the range of likely individual outcomes.

The result also does not answer whether fracture risk differed, because the primary endpoint is bone mineral density change rather than fractures. Although fracture counts are listed as a secondary outcome, numerical results are not reported in the registry record. Nor does the primary endpoint answer the disease-free survival question; numerical results for median disease-free survival are not reported in the registry record.

The registry’s description identifies a specific group of postmenopausal patients with operable primary breast cancer who had completed 4 to 6 years of adjuvant tamoxifen therapy. The result should not automatically be extended to other populations, treatment durations, bone sites, or outcomes. The trial was open-label, and details about missing data, adherence, analysis methods, and the original statistical plan are not reported. Those limitations constrain how completely the posted estimate can represent the full randomized trial experience.

Statistical evidence about a group-level outcome is not, by itself, a medical recommendation or a conclusion about an individual’s care. The record supports describing the observed bone-density comparison and its precision, while broader clinical conclusions require other evidence and context that are not reported in the registry record.

17. Why This Trial Matters Statistically

This trial illustrates why the endpoint definition and analysis population matter as much as the headline comparison. The primary outcome is a continuous measure of percent change in lumbar-spine bone mineral density, assessed at a specified follow-up time. Its interpretation depends on the measurement scale, the group means, their variability, and the participants included in the analysis.

The result also shows the value of reporting an estimate with a confidence interval rather than relying only on a p-value. The mean difference conveys the direction and magnitude of the contrast on the outcome’s scale, while the interval communicates statistical precision under the calculation’s assumptions. The p-value alone cannot convey either the size of the difference or its clinical importance.

At the same time, the record demonstrates the limits of registry summaries. The primary endpoint population is labeled intention-to-treat but is restricted to participants with measurements at both baseline and endpoint. The registry does not report a detailed participant flow, a missing-data analysis, the sponsor’s statistical model, or a multiplicity strategy. Those details are important for evaluating how robust an estimate is and how confidently secondary findings can be interpreted.

The secondary outcomes provide related information but also raise questions about multiple testing and outcome completeness. Similar directions across measures can be informative, yet unadjusted secondary comparisons should not be treated as independent confirmation of the primary result. The planning illustrations further show that sample-size needs depend strongly on the effect a study is designed to detect and on stated statistical assumptions; they do not reveal the original design justification.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary comparison is based on 21 participants in the letrozole group and 20 in the combination group, rather than all 83 enrolled participants. The endpoint description says that participants needed observations at baseline and endpoint. The registry record does not explain the difference between enrollment and these outcome counts, provide reasons for missing measurements, or show participant flow by arm. This limits assessment of how representative the endpoint analysis is of the randomized population.

The trial is described as open-label, with no masking. The record does not explain whether knowledge of treatment assignment could have influenced measurement, follow-up, or other aspects of outcome collection. It also does not report details of allocation concealment or randomization procedures. Randomized allocation is stated, but its implementation cannot be assessed from the registry summary.

The primary mean difference and associated interval and p-value are simple unadjusted recalculations from posted summary statistics. No sponsor analysis is listed, and the registry reports zero analyses. The original analysis plan, model specification, handling of baseline values, and assumptions used for inference are not reported. The recalculated comparison may therefore not reproduce an unreported planned analysis.

There is no reported multiplicity strategy for the several secondary outcomes and time points. Numerical results are not reported for all listed secondary outcomes, including fractures by visit and median disease-free survival. The adverse-event summaries do not explain causality, collection procedures, event duration, or the definition of the percentage denominator for the listed serious-event terms. Together, these gaps limit interpretation beyond the posted group summaries and prevent a complete appraisal of efficacy, safety, or robustness.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Safety/Efficacy of Letrozole Monotherapy or in Combination With Zoledronic Acid as Extended Adjuvant Treatment of Postmenopausal Patients With Primary Breast Cancer — NCT00332709.
• Registry record last updated 2011-11-16; status last verified 2011-10.
• Results first posted 2011-11-16.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

The registry describes a completed, randomized, open-label, parallel-group phase III trial with enrollment of 83. It compared 3 years of letrozole alone with 3 years of letrozole plus zoledronic acid every 6 months in postmenopausal patients with operable primary breast cancer after 4 to 6 years of adjuvant tamoxifen therapy.

The primary endpoint was percent change in lumbar-spine bone mineral density from baseline to month 36. The posted unadjusted mean difference was 0.14 percentage points, with a confidence interval from 0.071 to 0.209 and p < 0.001. The endpoint analysis included 21 participants in the letrozole group and 20 in the combination group.

Important details about the original analysis plan, missing data, multiplicity, and participant flow are not reported in the registry record. The result should be interpreted as a comparison of the posted endpoint summaries, rather than as a complete account of every trial outcome or every enrolled participant.