Safety and Pregnancy Outcomes in Thrombocythemia Patients Exposed to XAGRID® (Anagrelide Hydrochloride) Compared to Other Treatments: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Pregnancy Outcomes in Thrombocythemia Patients Exposed to XAGRID® (Anagrelide Hydrochloride) Compared to Other Treatments (NCT00567502), a registered phase not stated study. The primary outcome is Percentage of Participants With At Least One Pre-Defined Event (PDE), Deaths, Pregnancies.

2. Clinical Question

3. Trial Design

This was a non-interventional, post-authorisation safety study of people with essential thrombocythemia exposed to Xagrid or other conventional cytoreductive treatments. The registry describes the study as taking place in Europe and as continuously monitoring safety and pregnancy outcomes. It is marked completed. The recorded start date is 2005-05-31, and the primary completion date is 2014-04-30.

The brief description planned to enrol at least 750 subjects taking Xagrid and up to 3000 taking other cytoreductive therapies. The recorded enrollment is 3647. The planned follow-up was 5 years for each enrolled patient, focused on pre-defined events and suspected serious adverse reactions. The outcome timeframe for the primary measure is up to 5 years.

The registry describes treatment categories for XAGRID®, Xagrid plus other cytoreductive therapy, and other cytoreductive therapy. This is not a randomized comparison: the registry record says allocation was not stated and the arms are not a like-for-like control comparison. Treatment groups therefore represent observed treatment exposure, not groups formed by random assignment. Differences between groups could reflect differences in who received each treatment, their clinical circumstances or their follow-up, as well as any treatment-related differences.

The primary population was the First Treatment Safety Population, defined as participants who received cytoreductive therapy at registration. However, events and assessments were allocated to the treatment a participant was receiving at the time of the event or assessment. These descriptions identify different aspects of the registry’s population and exposure handling; they do not provide a detailed statistical analysis plan. Details of recruitment procedures, treatment selection, adjustment for baseline differences and handling of follow-up interruptions 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: Due to the non-interventional nature of the study, participants could be receiving XAGRID, XAGRID+Other (Cytoreductives), other (cytoreductives) and no essential thrombocythemia (ET) therapy. During the study participants could change the treatments.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: First Treatment Safety Population included participants who received cytoreductive therapy at registration. All events/data were allocated to the treatment that a participant was receiving at the time of the event/assessment.

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: First Treatment Safety Population included all participants who received at least 1 dose of cytoreductive treatment. Data of 2 participants were missing in the Other (Cytoreductives) treatment arm.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With At Least One Pre-Defined Event (PDE), Deaths, Pregnancies, measured over Up to 5 years.

The primary outcome is the percentage of participants with at least one pre-defined event (PDE), death or pregnancy over a timeframe of up to 5 years. It describes the proportion of participants experiencing an outcome of interest, rather than the total number of episodes or the timing of each event. The registry’s definition treats a non-PDE death as a death not recorded as the outcome of another PDE.

PDEs were evaluated when an event occurred. A panel of independent qualified physicians, blinded to cytoreductive therapy, validated each PDE before analysis. This review is intended to apply a clinical definition of the events consistently without the panel knowing the participant’s treatment category. Blinding of the panel does not make treatment allocation random, and it does not remove differences in the populations receiving each therapy.

Such an endpoint is used in safety monitoring to describe how often specified events arise among exposed participants, including outcomes that may be uncommon or clinically important. Combining event, death and pregnancy information in the primary outcome gives a broad account of the outcomes the study set out to monitor. It does not, by itself, explain which component accounts for a result, distinguish recurrent events from a participant’s first event, or establish that treatment caused an outcome. The primary outcome result and its component-specific results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General statistical context. A percentage of participants with an event is a participant-level measure: it concerns whether a participant experienced the specified outcome during the defined observation period. It differs from an event rate, which ordinarily relates event occurrences to time at risk. The registry includes both a primary percentage outcome and a secondary outcome called the event rate of thrombohaemorrhagic events, but the registry record does not report the numerical primary result or a detailed method for estimating the secondary rate.

What does the primary measure summarize?

The primary measure concerns participants with at least one PDE, death or pregnancy over up to 5 years. The focus on whether a participant experienced an outcome makes the measure a proportion of participants, not a count of all repeated occurrences. The record defines how non-PDE deaths were handled: only deaths not recorded as the outcome of another PDE were included as non-PDE deaths. It does not report the observed proportion, separate component results or a confidence interval. Those omissions prevent assessment of the magnitude and precision of the primary outcome.

The registry says that PDEs were evaluated whenever an event occurred and validated by an independent panel of qualified physicians blinded to cytoreductive therapy. In general, independent blinded event review can reduce the possibility that knowledge of treatment influences whether an event meets a definition. It cannot correct for differences in treatment selection, event reporting or follow-up, and it does not make an observational comparison equivalent to a randomized trial.

How should the treatment categories be understood?

The recorded categories include XAGRID®, Xagrid plus other cytoreductive therapy, and other cytoreductive therapy. The primary population includes participants who received cytoreductive therapy at registration, while events and assessments were allocated to the treatment being received when they occurred. This means the outcome allocation follows treatment at the event or assessment, according to the registry description. The record does not report further details on how treatment changes, overlapping exposure or time between assessments were handled.

In an observational study, treatment is not assigned at random. People receiving different therapies may differ in ways related to both treatment choice and outcome. General statistical methods can attempt to adjust for measured differences, but the record does not report a covariate-adjustment method, a propensity-score method or another approach to confounding. No adjusted comparison should therefore be inferred from the registry entry.

What do the serious-event counts convey?

The safety entries report 37 affected among 1300 at risk in the XAGRID group and 70 affected among 3069 at risk in the Other (Cytoreductives) group. They are descriptive counts alongside group denominators. Comparing counts without considering the study design, follow-up and participant differences would be misleading. Even a direct comparison of proportions would not address confounding or establish causation. No adjusted safety effect, uncertainty interval or test result is reported in the registry record.

The top serious-event terms are presented with percentages, including Atrial fibrillation, 0.5%, and Anaemia, 0.3%. The remaining listed terms and percentages are Cardiac failure Congestive, 0.2%; Palpitations, 0.2%; Gastrointestinal haemorrhage, 0.2%; and Epistaxis, 0.2%. The record does not report enough detail alongside these terms to determine their treatment-specific denominators or to make an adjusted comparison. These percentages should be treated as descriptive entries rather than estimates of comparative treatment effects.

What can confidence intervals and over-dispersion add?

General statistical explanation. A confidence interval communicates uncertainty around an estimate, with a narrower interval indicating greater precision under the method’s assumptions. It does not remove bias from non-random treatment allocation. The registry record does not report confidence intervals for the primary result or for the serious-event comparison, so precision cannot be assessed from those entries.

Over-dispersion is a general issue for count data when variability exceeds what a simple statistical model expects. If it is present, a model that ignores it can understate uncertainty. The registry lists an event-rate outcome for thrombohaemorrhagic events but does not report a model, dispersion assessment or related adjustment. It is therefore not possible to say whether over-dispersion was assessed or how the event-rate outcome was analyzed.

What does the planning illustration mean?

Any sample-size figures associated with planning are illustrations based on the observed effect, not the study’s own design justification and not observed power. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the target effect is a stated fraction of the observed effect. In general, a planning illustration describes the sample size implied by assumptions about a target effect and testing procedure. It does not show that a study had a particular probability of detecting an effect after it was completed. The registry record does not report the trial’s own sample-size justification, and the primary result needed to interpret an observed-effect illustration is not reported.

10. Multiplicity, Missing Data and Analysis Populations

The registry records six outcome measures, including the primary outcome and secondary measures such as thrombohaemorrhagic event rate, platelet count, duration of exposure for each ET therapy and cumulative dose for each ET therapy. Multiple outcome measures can create a multiplicity issue when many statistical tests are conducted: the chance of at least one apparently notable finding may increase as the number of tests grows. This is a general concern, not evidence that a particular testing problem occurred in this study.

The record lists no analyses and does not report a multiplicity strategy, such as a prespecified hierarchy, adjustment across outcomes or a rule for interpreting exploratory results. It also does not report whether any interim analyses were planned or conducted. Details of the statistical plan and any correction for multiple comparisons are not reported in the registry record. In the absence of reported estimates and tests, readers cannot determine which outcomes were formally tested or how multiplicity was handled.

Missing-data methods and analysis populations beyond the First Treatment Safety Population are not reported in the registry record. The registry defines that population as participants who received cytoreductive therapy at registration and says events and assessments were allocated to the treatment received at the time. It does not explain the handling of incomplete follow-up, missing outcome assessments, loss to follow-up or participants who changed treatments. The planned follow-up was 5 years for each enrolled patient, but the registry entry does not establish that all participants completed that follow-up.

These gaps matter because missing outcomes and unequal observation can affect the interpretation of participant percentages and event rates. They also limit assessment of whether the posted safety counts represent comparable observation periods. No imputation method, sensitivity analysis or missingness assessment is reported in the registry record.

11. 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 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: atrial fibrillation (0.5%), anaemia (0.3%), cardiac failure congestive (0.2%), palpitations (0.2%), gastrointestinal haemorrhage (0.2%).

The registry’s serious-event entries list 37 affected among 1300 at risk for XAGRID and 70 affected among 3069 at risk for Other (Cytoreductives). These figures describe the recorded safety entries; they are not, by themselves, a controlled estimate of comparative risk. The study was non-interventional, allocation was not stated, and the registry cautions that the treatment categories are not a like-for-like control comparison. The record does not report adjusted estimates or uncertainty intervals for these counts.

The listed serious-event terms are Atrial fibrillation, 0.5%; Anaemia, 0.3%; Cardiac failure Congestive, 0.2%; Palpitations, 0.2%; Gastrointestinal haemorrhage, 0.2%; and Epistaxis, 0.2%. These are descriptive percentages; the registry entry does not report enough detail to interpret them as treatment-specific comparative results.

Death values are not reported in the registry record. That is not evidence of no deaths. The primary outcome separately concerns PDEs, deaths and pregnancies, but its results are not reported. Safety counts should therefore be read as limited descriptive information, not as a complete assessment of safety or proof of a treatment effect.

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

The registry record establishes that a completed, non-interventional post-authorisation safety study was conducted in people with essential thrombocythemia exposed to Xagrid and other cytoreductive treatments. It records enrollment of 3647 and describes planned follow-up of 5 years for each patient, with attention to pre-defined events and suspected serious adverse reactions. It also documents a process in which an independent panel blinded to cytoreductive therapy validated pre-defined events before analysis.

The posted results do not report the primary percentage of participants with at least one pre-defined event, death or pregnancy. Without that result, readers cannot determine the observed frequency of the primary outcome or its precision. The available serious-event entries provide descriptive figures for the XAGRID and Other (Cytoreductives) categories, but do not supply adjusted comparative effects or uncertainty estimates. The registry’s warning that the arms are not a like-for-like control comparison is important when interpreting any apparent difference.

The record does not establish that XAGRID® caused, prevented or changed the likelihood of any outcome. Observational treatment groups can differ for reasons related to treatment choice and health status, and those differences can affect outcomes. The presence of a blinded event-validation process addresses event classification, not those sources of confounding.

Nor does the absence of a posted primary result mean that no events occurred or that the outcome was assessed as unimportant. It means that the registry record does not report the result needed to answer the primary question. The record also does not report the statistical analysis plan, a sample-size justification, methods for missing data, interim analyses or a multiplicity approach. Conclusions should stay within the evidence actually recorded: a completed observational study with defined safety outcomes and a limited set of descriptive safety entries.

13. Why This Trial Matters Statistically

This study illustrates why a registry entry’s design and results need to be read together. A substantial recorded enrollment of 3647 and a completed status describe the scope and administrative state of the study, but they do not tell readers whether the primary outcome occurred frequently or how precisely it was estimated. The absence of the primary result is consequential: the principal safety question cannot be evaluated from the posted record.

The study also highlights a core challenge in observational comparisons. People receiving XAGRID®, a combination of Xagrid and other cytoreductive therapy, or other cytoreductive therapy were not assigned randomly. The registry says allocation was not stated and the arms are not a like-for-like control comparison. Thus, even clearly reported group counts do not automatically yield a fair estimate of treatment differences. Differences in patient characteristics, clinical reasons for treatment, exposure and follow-up can all complicate interpretation.

At the same time, the event-validation process is methodologically relevant. An independent panel blinded to cytoreductive therapy validated PDEs, which can support consistent classification of those outcomes. This safeguard should be understood in its proper scope: it does not address confounding or replace the missing comparative analysis.

Finally, the record separates several kinds of information that are often conflated: enrollment, an outcome definition, safety counts, and inferential results. Enrollment is not evidence of precision; outcome definitions are not outcome estimates; and descriptive safety entries are not causal findings. Clear reporting of analysis methods, missing-data handling and uncertainty would be needed to support stronger statistical interpretation. Those details are not reported in the registry record.

14. 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.

Several limitations specific to this study constrain interpretation. First, the registry describes the study as non-interventional, and states that allocation was not stated. It explicitly cautions that the treatment arms are not a like-for-like control comparison. Treatment choice may therefore be associated with participant characteristics and clinical circumstances that also relate to outcomes. The registry does not report adjustment methods that would address measured confounding.

Second, the primary outcome result is not reported in the registry record. Although the outcome is defined as the percentage with at least one PDE, death or pregnancy over up to 5 years, no estimate or uncertainty interval is posted. The record also does not give component-specific results for PDEs, deaths and pregnancies. The listed serious-event counts cannot substitute for the missing primary result.

Third, the exposure description allocates events and assessments to the treatment received at the time. The registry does not report additional detail about treatment changes, concurrent exposure, exposure duration in the primary analysis or the treatment of follow-up after a change. The First Treatment Safety Population is defined by therapy at registration, but details on how that population definition interacts with subsequent exposure are not reported.

Fourth, the registry record does not describe missing-data methods, follow-up completeness, statistical adjustment, confidence intervals, formal tests, interim analyses or multiplicity handling. Although planned follow-up was 5 years for each patient, the record does not establish that every participant had complete follow-up. The death values in the safety entries are not reported in the registry record; they should not be interpreted as zero.

Finally, the serious-event terms and percentages are not accompanied by enough information to establish treatment-specific comparative estimates. These limitations mean the posted safety information should be treated as descriptive, with no causal conclusion inferred from between-group figures.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Safety and Pregnancy Outcomes in Thrombocythemia Patients Exposed to XAGRID® (Anagrelide Hydrochloride) Compared to Other Treatments — NCT00567502.
• Registry record last updated 2021-06-09; status last verified 2021-05.
• Results first posted 2015-11-17.
• 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.

18. Record Summary

This completed European non-interventional post-authorisation safety study concerns essential thrombocythemia patients exposed to XAGRID® or other cytoreductive treatments. The recorded enrollment is 3647; the study dates are 2005-05-31 to primary completion on 2014-04-30. Planned follow-up was 5 years per patient. The primary outcome concerns participants with at least one pre-defined event, death or pregnancy, with PDEs validated by an independent panel blinded to treatment.

The primary outcome result is not reported in the registry record. Serious-event entries list 37 affected among 1300 at risk for XAGRID and 70 among 3069 at risk for Other (Cytoreductives), alongside descriptive serious-event terms and percentages. The registry states that allocation was not stated and that the arms are not a like-for-like control comparison. No analyses are listed, and the record does not report adjusted comparative estimates, uncertainty intervals or the detailed statistical plan.