A Study Evaluating the Efficacy and Safety of Mitapivat in Participants With Transfusion-Dependent Alpha- or Beta-Thalassemia (α- or β-TDT): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study Evaluating the Efficacy and Safety of Mitapivat in Participants With Transfusion-Dependent Alpha- or Beta-Thalassemia (α- or β-TDT) (NCT04770779), a randomized phase 3 study. The primary outcome is Double-blind Period: Percentage of Participants Who Achieved Transfusion Reduction Response (TRR).

2. Clinical Question

3. Trial Design

The registry describes a Phase 3, randomized, double-blind, placebo-controlled, multicenter study of mitapivat in participants with transfusion-dependent alpha- or beta-thalassemia. It used a parallel-group design and quadruple masking. The registry record lists enrollment as 258 and identifies Agios Pharmaceuticals, Inc. as the sponsor.

The double-blind comparison lasted 48 weeks. Participants assigned to mitapivat received 100 mg orally twice daily; those assigned to placebo received matching placebo on the same schedule. The registry describes an open-label extension lasting up to 5 years, during which participants in both groups could receive mitapivat. The primary result discussed in this analysis concerns the double-blind period, not the extension.

The study began on 2021-11-30, and the listed primary completion date is 2024-04-11. Its status in the registry record is active, not recruiting. Those registry entries describe the study’s recorded status and timeline; they do not establish that all follow-up or reporting is complete.

The primary objective was to compare mitapivat with placebo on transfusion burden. The posted primary endpoint was the percentage of participants achieving transfusion reduction response through Week 48. The FAS included all randomized participants, and the posted arm counts for the primary result were 171 for mitapivat and 87 for placebo. The registry record does not report the original sample-size justification or the full statistical analysis plan.

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: A total of 305 participants with a diagnosis of Transfusion-Dependent Alpha- or Beta-Thalassemia (α- or β-TDT) were screened. Of which, 258 were randomized and 257 received study treatment in this study.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: FAS included all participants who were randomized.

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.

Population: Full analysis set (FAS) included all participants who were randomized.

6. Primary Endpoint

The registry lists the primary outcome as Double-blind Period: Percentage of Participants Who Achieved Transfusion Reduction Response (TRR), measured over Double-blind Period: Baseline through Week 48.

The primary endpoint is the percentage of participants who achieved transfusion reduction response (TRR) during the double-blind period from baseline through Week 48. It is a binary outcome: each participant is classified as a responder or nonresponder, and the arm result is expressed as a percentage of participants.

The registry defines TRR as a reduction of at least 50% in transfused red blood cell units, together with a reduction of at least 2 units, in any consecutive 12-week period through Week 48. The comparison is against baseline transfusion burden standardized to 12 weeks. The record describes baseline burden as using the total red blood cell units transfused during the 24-week period before randomization for participants randomized but not dosed, or before study treatment began for participants randomized and dosed. Participants who withdrew before Week 12 (Day 85) were considered nonresponders.

This kind of endpoint is used to assess whether transfusion burden has meaningfully decreased relative to a participant’s baseline, rather than relying on a single transfusion measurement. As a general statistical point, a binary response outcome is easy to interpret as a proportion, but it compresses the degree and timing of individual changes into responder or nonresponder categories. The registry record does not report further rationale for selecting this endpoint.

7. Results Posted in the Registry

• Mitapivat: 30.4% (52/171) versus 12.6% (11/87) on control; risk difference 17.8 percentage points (95% CI 8.0 to 27.6), risk ratio 2.41 (1.32–4.37); unadjusted two-proportion z-test p = 0.002.

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.

Double-blind Period: Percentage of Participants Who Achieved TRR2

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Mitapivat: 13.5% (23/171) versus 2.3% (2/87) on control; risk difference 11.2 percentage points (95% CI 5.1 to 17.2), risk ratio 5.85 (1.41–24.25); unadjusted two-proportion z-test p = 0.004.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Mitapivat than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Double-blind Period: Percentage of Participants Who Achieved TRR3

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Mitapivat: 14.6% (25/171) versus 1.1% (1/87) on control; risk difference 13.5 percentage points (95% CI 7.7 to 19.2), risk ratio 12.72 (1.75–92.31); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Mitapivat than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Double-blind Period: Percentage of Participants Who Achieved TRR4

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Mitapivat: 7.6% (13/171) versus 1.1% (1/87) on control; risk difference 6.5 percentage points (95% CI 1.9 to 11.0), risk ratio 6.61 (0.88–49.73); unadjusted two-proportion z-test p = 0.031.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Mitapivat than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The reported secondary binary response outcomes follow the same general direction as the primary result: the responder percentages are higher in the mitapivat group across the posted TRR threshold outcomes. This directional consistency supports the view that the primary pattern is not isolated to a single response definition. The secondary findings remain supportive rather than substitutes for the prespecified primary comparison.

The registry lists other secondary outcomes concerning red blood cell units, transfusion independence, and iron-related measures. Their results and statistical details are not described in the posted endpoint results summarized in this analysis, so no conclusion about their direction or magnitude is drawn. Outcomes listed in the registry should not be treated as having the same evidential status when their estimates and uncertainty are not available for evaluation.

Secondary endpoints are often tested alongside a primary endpoint. As a general statistical principle, testing many outcomes increases the chance that at least one result will appear statistically notable by chance if no adjustment or other testing strategy is used. The registry record does not report whether secondary p-values were adjusted for multiplicity or how the testing sequence was controlled. Therefore, unadjusted secondary results carry less weight than the primary analysis and should be interpreted cautiously.

The registry reports 19 secondary outcomes posted, but the full analysis plan and multiplicity strategy are not reported in the registry record. The consistent direction across the reported threshold outcomes is useful context, but it does not establish that every secondary outcome was confirmed or that the overall set of findings is free from selective emphasis.

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

• Double-blind Period: Percentage of Participants Who Achieved TRR2
• Double-blind Period: Percentage of Participants Who Achieved TRR3
• Double-blind Period: Percentage of Participants Who Achieved TRR4
• Double-blind Period: Percent Change From Baseline in Transfused RBC Units
• Double-blind Period: Percentage of Participants Who Achieved Transfusion-Independence
• Double-blind Period: Change From Baseline in Iron Levels
• Double-blind Period: Change From Baseline in Serum Ferritin Levels
• Double-blind Period: Change From Baseline in Total Iron Binding Capacity

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is binary because each randomized participant either met the registry’s TRR definition or did not. The reported arm percentages describe the proportion classified as responders in each group. Comparing these proportions is one way to summarize the randomized comparison. The posted analysis reports a common risk difference, which expresses the absolute difference in response rates on the percentage-point scale.

What a risk difference conveys

A risk difference compares two proportions by expressing how far apart they are on an absolute scale. In this study, the sponsor reports a Mantel-Haenszel common risk difference of 17.6 percentage points. It describes the estimated separation between the groups’ response rates under that method. It is not a relative measure such as a risk ratio, and it does not mean that every participant experienced a change of that size.

The registry also contains a recalculated, unadjusted risk difference of 0.178, with an interval from 0.080 to 0.276. That calculation is based on posted summary statistics and does not replace the sponsor’s analysis. The sponsor’s result is the reported analysis; the recalculation is useful as a check on the broad comparison, not as a reconstruction of all trial-level modeling or adjustment.

What the Mantel-Haenszel method means

The registry identifies the sponsor’s method as Mantel-Haenszel and labels the parameter as a common risk difference on response rate. In general, Mantel-Haenszel methods combine information across strata to estimate an overall association or difference while accounting for the stratification used in an analysis. The registry record does not report the strata or additional implementation details for this analysis, so the precise mechanics of the sponsor’s calculation cannot be fully assessed from the record alone.

Randomization is intended to make the assigned groups comparable on average, while masking is intended to reduce the influence of knowledge of assignment on participant care and outcome assessment. The record identifies the study as randomized and quadruple-masked. It does not specify which roles were masked, so that detail is not inferred.

How to read the p-value

The reported p-value is < 0.001. In general, a p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the analysis assumptions were true. It is not the chance that the treatment has no effect, nor is it a measure of clinical importance. The registry record does not report the complete prespecified testing strategy or whether this result was adjusted for testing multiple outcomes.

The primary result is based on the FAS, defined in the registry as all randomized participants. The endpoint rule specifically classifies participants who withdrew before Week 12 (Day 85) as nonresponders. Other details of missing-outcome handling are not reported in the registry record. This distinction matters: an explicit rule for early withdrawal does not by itself describe how every other incomplete or unavailable assessment was handled.

Why binary outcomes require context

As a general statistical consideration, a responder endpoint can simplify communication but depends on the chosen threshold. Participants near either side of the threshold may be classified differently despite similar underlying changes, while people with different magnitudes of response may receive the same responder classification. The definition includes both a percentage reduction and an absolute reduction in transfused units, and specifies an eligible period for response.

Confidence intervals express uncertainty in an estimated effect, while the p-value addresses compatibility with a null hypothesis under a particular analysis. Neither provides a complete account of bias, generalizability, missingness, or the importance of an outcome to participants. The registry record does not report a detailed statistical analysis plan, original sample-size justification, interim analyses, or the full missing-data strategy. These omissions limit independent evaluation of some analytic choices, even though the reported endpoint, population definition, and sponsor analysis are stated.

11. Confidence Intervals and Precision

The sponsor’s primary estimate is a common risk difference of 17.6 percentage points, with a 95% confidence interval from 8.0 to 27.2. The interval indicates the range of values reasonably compatible with the sponsor’s analysis under its statistical assumptions. It gives a sense of precision: a narrower interval would indicate less uncertainty about the estimated difference, while a wider interval would indicate more.

The interval is entirely above zero, the value corresponding to no difference on the risk-difference scale. The reported p-value is < 0.001, consistent with that interval-based comparison. These are related summaries of uncertainty, not independent evidence. The interval also conveys more information than a threshold-based declaration because it presents a range of plausible effect sizes.

The recalculated unadjusted estimate is 0.178, with an interval from 0.080 to 0.276. The sponsor’s estimate and the recalculated estimate are close in scale and direction, while they arise from different methods. The registry record does not supply further detail on the construction of the recalculated interval. The sponsor’s reported analysis remains the appropriate result to prioritize.

As a general point, confidence intervals do not guarantee that the true effect lies within the displayed range, and they do not account for every possible source of bias or uncertainty. They quantify statistical uncertainty under the analysis assumptions. The confidence interval does not show variation in individual responses, and the arm percentages alone do not convey how precisely each percentage is estimated.

The registry reports no arm-specific confidence intervals for the percentages. It also does not report subgroup-specific precision for the primary endpoint. Interpretation therefore centers on the reported between-group estimate and its interval, rather than on unreported subgroup or individual-level estimates.

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 illustrations based on the observed effect, not a record of the trial’s original design calculations. For the binary outcomes, the figures are participants per arm, not total events. The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set at the stated fraction of the observed effect.

The 80% power column describes the planned number of participants per arm that would yield 80% probability of detecting the specified effect under those assumptions, if that effect and the other assumptions were correct. The 90% power column uses a higher target probability of detecting the same specified effect and therefore generally calls for more participants per arm. These are prospective planning concepts, not properties that can be read back from the trial’s observed result.

Rows planning for 100%, 75%, and 50% of the observed effect use progressively smaller target effects. Smaller effects are harder to distinguish from random variation, so they require more participants per arm to reach the same target power. The displayed figures depend on the planning assumptions and should not be treated as a universal requirement for another trial.

The original design assumptions and sample-size justification are not reported in the registry record. The planning figures are not observed power.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.126; treatment proportion p₁ = 0.304; average p̄ = 0.215.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5813 = 1.1392.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5675 = 0.4776.
4. n = (1.1392 + 0.4776)² / (0.1777)² = 82.8, rounded up to 83 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
p0 <- 0.126436781609195                          # control proportion
p1 <- 0.304093567251462                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(4770779)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 83 (80% power), 111 (90% power)
 75% of observed effect: n per arm = 137 (80% power), 183 (90% power)
 50% of observed effect: n per arm = 281 (80% power), 376 (90% power)
power.prop.test: 82.8 
Simulated power at n = 83 per arm: 0.815 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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. Analyses Reported by the Sponsor

The sponsor’s own primary analysis is a Mantel-Haenszel common risk difference of 17.6 percentage points, with a 95% confidence interval from 8.0 to 27.2 and p < 0.001. The registry also includes an unadjusted recalculation from the posted summary statistics: a risk difference of 0.178, with an interval from 0.080 to 0.276. The discrepancy flag is false, and the two estimates are broadly similar in direction and scale.

The recalculation is not a replacement for the sponsor’s analysis. It does not recreate the full trial data or necessarily reproduce any stratification or other analysis details used by the sponsor. The sponsor’s reported analysis takes precedence when describing the trial’s formal result. The recalculation is best understood as a simple independent check using the posted arm summaries.

The sponsor reports a superiority analysis. That label describes the stated analysis type; it does not by itself resolve questions about missing data, multiplicity, or the broader clinical meaning of the result. Those considerations remain relevant when interpreting the finding.

15. Multiplicity, Missing Data and Analysis Populations

The primary analysis population is described as the FAS, including all randomized participants. The endpoint definition also specifies that participants withdrawn before Week 12 (Day 85) were considered nonresponders. This makes the handling of that particular situation explicit, but it does not fully describe the treatment of every missing measurement, later withdrawal, or incomplete follow-up.

Other missing-data procedures are not reported in the registry record. The record does not state how missing endpoint assessments after the early-withdrawal window were handled, whether any sensitivity analyses were conducted, or how departures from the intended treatment period affected the analysis. Without those details, the robustness of the result to alternative missing-data assumptions cannot be assessed from the registry entry alone.

The registry includes multiple secondary outcomes, and 19 secondary outcomes are listed as posted. The multiplicity strategy—whether outcomes were arranged in a hierarchy, adjusted for multiple testing, or treated as exploratory—is not reported in the registry record. In general, testing many outcomes without an appropriate strategy can increase the chance of false-positive findings. This is why the primary endpoint and its reported analysis generally carry more inferential weight than unadjusted secondary results.

The original sample-size justification, full statistical analysis plan, and details of any interim analyses are not reported in the registry record. Their absence should not be interpreted as evidence that such procedures were or were not used. Rather, it limits an external reader’s ability to verify the planned analysis, assess deviations from it, and understand how precision and testing decisions were determined before results were known.

The randomized design and FAS definition provide important context, but they do not answer all questions about missingness, multiplicity, or analysis choices. These limits do not negate the posted estimate; they identify areas where the registry record does not permit a complete assessment.

16. Safety Results

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

Deaths

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: pneumonia (2.4%), viral infection (1.2%), splenic haematoma (1.2%), cholecystitis (1.2%), cholecystitis acute (1.2%).

The registry reports serious adverse events for 19 participants in the mitapivat safety group, with 172 at risk, and for 13 participants in the placebo safety group, with 85 at risk. It reports zero deaths in each group. These are counts of participants affected and at risk as recorded; they should not be converted into a comparative safety conclusion without the relevant analysis and context.

The listed serious adverse event terms include pneumonia at 2.4%, viral infection at 1.2%, splenic haematoma at 1.2%, cholecystitis at 1.2%, cholecystitis acute at 1.2%, and cholangitis acute at 1.2%. The registry also reports other adverse events affecting 122 participants in the mitapivat group and 50 in the placebo group, with 172 and 85 at risk, respectively.

As a general point, serious adverse event counts do not by themselves show whether an event was caused by a study drug. They also do not convey timing, duration, recurrence, exposure-adjusted rates, or the full clinical context. The registry record does not report those details in the safety information. Safety interpretation should therefore remain descriptive and separate from the efficacy comparison.

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

The primary result describes a higher observed percentage of TRR responders in the mitapivat group than in the placebo group during the 48-week double-blind period. The sponsor’s estimated difference and confidence interval quantify the comparative result and its statistical uncertainty under the reported method. This is evidence about the specific endpoint, population, treatment schedule, and period studied.

It does not mean that every participant receiving mitapivat achieved a response, or that participants classified as nonresponders had no change at all. The endpoint reduces individual changes to a responder classification based on a specified threshold and time window. The posted percentages do not describe the full distribution of transfusion burden changes.

The result also does not establish effects on every outcome named in the registry. The registry lists additional secondary outcomes, but the available record and results do not support claims about outcomes whose estimates are not presented. Nor does the double-blind-period comparison establish what happened during the open-label extension, when the treatment arrangements differed from the randomized comparison.

A statistically notable result is not synonymous with a judgment about clinical importance. The confidence interval indicates uncertainty in the estimated group difference, while decisions about the importance of a change require context beyond the p-value. The registry record does not report a threshold for interpreting the clinical importance of the between-group difference.

Finally, the result should not be interpreted as individualized guidance. It is a group-level analysis from a randomized trial, with limitations in the registry’s reporting of missing-data procedures, multiplicity, and the full analysis plan. The posted findings describe the trial result; they do not determine how an individual should be treated.

18. Why This Trial Matters Statistically

This trial illustrates why an absolute comparison can be more informative than a p-value alone. The sponsor’s common risk difference expresses the estimated separation between response rates in percentage points, while the confidence interval communicates the uncertainty around that estimate. Together with the arm percentages, these measures show both the observed pattern and its precision without reducing interpretation to whether a threshold for statistical significance was crossed.

The endpoint also illustrates the analytic consequences of defining response in advance. TRR combines a relative reduction with a minimum reduction in transfused units and places response within a specified time window. Those rules make the outcome interpretable, but they also mean that the result depends on the operational definition of response. A binary endpoint can mask differences in the degree of improvement among responders and nonresponders.

The registry’s reporting permits readers to distinguish the sponsor’s Mantel-Haenszel result from a simple unadjusted recalculation. That distinction matters: a reanalysis of summary statistics can check the broad pattern but cannot replace the analysis reported by the sponsor or recover unreported modeling details. Here the two estimates are broadly aligned, and the sponsor result remains the primary reported analysis.

The case also highlights the importance of transparent reporting. The endpoint and analysis population are described, but the original sample-size justification, full missing-data strategy, multiplicity plan, and other analysis details are not reported in the registry record. Those details help readers evaluate how the analysis was planned and how robust secondary findings may be.

19. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The registry record does not report the full statistical analysis plan, original sample-size justification, or details of any interim analyses. It also does not describe the strata or other implementation details behind the sponsor’s Mantel-Haenszel analysis. These omissions constrain independent assessment of how closely the reported analysis followed the study’s prespecified methods.

Missing-data handling is only partly described. Participants who withdrew before Week 12 (Day 85) were classified as nonresponders, but other missing-outcome procedures and sensitivity analyses are not reported in the registry record. That leaves uncertainty about the effect of later withdrawals or unavailable assessments on the result.

The registry does not report the strategy used to account for testing multiple secondary outcomes. The secondary findings therefore require caution, particularly when interpreted separately from the primary endpoint. The reported responder outcomes are also binary and depend on the specified TRR threshold; they do not capture the full range of individual changes in transfusion burden.

The primary result concerns the double-blind period through Week 48. It does not establish outcomes during the open-label extension, and the registry information does not provide a full account of longer-term comparative efficacy. Safety counts are descriptive and are not accompanied by exposure-adjusted comparisons or detailed event timing. These are limitations of what can be concluded from the registry record, not evidence that unreported analyses or information do not exist elsewhere.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: A Study Evaluating the Efficacy and Safety of Mitapivat in Participants With Transfusion-Dependent Alpha- or Beta-Thalassemia (α- or β-TDT) — NCT04770779.
• Registry record last updated 2026-10-28; status last verified 2026-10.
• Results first posted 2025-05-25.
• 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.

23. Record Summary

NCT04770779 is a Phase 3 randomized, double-blind, placebo-controlled, multicenter parallel-group study of mitapivat in transfusion-dependent alpha- or beta-thalassemia. The primary endpoint was the percentage achieving TRR from baseline through Week 48 during the double-blind period. The FAS included all randomized participants, and early withdrawal before Week 12 (Day 85) was classified as nonresponse.

The posted response percentages were 30.4% for mitapivat and 12.6% for placebo. The sponsor reported a Mantel-Haenszel common risk difference of 17.6 percentage points, with a 95% confidence interval from 8.0 to 27.2 and p < 0.001. The registry record does not report the complete analysis plan, original sample-size justification, full missing-data strategy, or multiplicity approach. Results should be interpreted within the endpoint definition and double-blind period.