This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for AirXpanders AeroForm Tissue Expander System for Breast Reconstruction (NCT02504424), a na na study. The primary outcome is Number of Breasts With Successful Tissue Expansion With Exchange to a Permanent Breast Implant Unless Exchange is Precluded by a Non-device Related Event.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02504424 |
| Phase | NA |
| Condition | Breast Cancer |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 50 |
| Arms in the primary outcome | n/a |
| Lead sponsor | AirXpanders, Inc. |
| Results posted | Yes |
2. Clinical Question
Population
People with breast cancer undergoing breast reconstruction with the AeroForm Tissue Expander. The registry reports 50 treated participants; the primary endpoint is analyzed per breast, rather than per participant.
Intervention
AeroForm Tissue Expander inflation with carbon dioxide by remote control. The intervention is a device, and the study is described as single group.
Comparator
There is no parallel comparator group in the registry record. The allocation field is listed as NA, and the study is not a randomized comparison.
Primary question
At the 6-month timeframe, how many breasts had successful tissue expansion followed by exchange to a permanent breast implant, except when exchange was precluded by a non-device-related event? Device-related adverse events or device malfunction leading to expander removal or replacement count as failures.
This question focuses on a defined treatment pathway: expansion with the study device and subsequent exchange to a permanent implant. The endpoint is a count of breasts meeting that success definition, not a comparison of average outcomes between treatment groups. The registry says the primary endpoint is analyzed per breast, so a participant can contribute more than one breast to the endpoint.
The record reports an analysis population of 48 participants and 80 breasts for the primary endpoint. It also describes exclusions associated with a participant who failed exchange of both breasts for a non-device-related reason and a participant who withdrew. The breast-level population description is incomplete in the registry record, so the full accounting of exclusions is not reported there. The posted primary result itself is not reported in the registry record, preventing assessment of how many breasts met the endpoint definition.
3. Trial Design
The study is registered as NCT02504424 and is titled AirXpanders AeroForm Tissue Expander System for Breast Reconstruction. The official title identifies it as XPAND-II. AirXpanders, Inc. is listed as the sponsor. The condition is breast cancer, and the intervention is the AeroForm Tissue Expander, classified as a device.
The registry describes a single-group study with no masking. Allocation is listed as NA, and the study is not a randomized comparison. The arm description states that the AeroForm Tissue Expander is inflated with carbon dioxide by remote control. Although the record uses an arm label for the device, it does not describe a separate control arm. Consequently, the study design does not provide a concurrent group receiving a different device or another treatment for a like-for-like comparison.
The enrollment is 50. The phase is listed as NA. The recorded study start is 2015-11-12, primary completion is 2017-05-03, and status is COMPLETED. The brief summary says the study was designed to allow existing investigators continued access to the AeroForm Tissue Expander while AirXpanders completed a marketing application and during FDA review. The registry does not report further detail on how that purpose shaped the endpoint or analysis.
The primary endpoint is assessed at 6 months and counts breasts, with a success definition based on tissue expansion and exchange to a permanent breast implant. The endpoint treats removal or replacement of an expander due to device-related adverse events or device malfunction as failure. The record also lists a secondary outcome concerning successful expansion with exchange in the per-protocol cohort. Further details about the secondary analysis population and its result are not reported in the registry record.
Sample-size justification, planned interim analyses, and a detailed statistical analysis plan are not reported in the registry record. The design therefore supports a descriptive account of outcomes in the study group, but the record does not establish a randomized treatment contrast.
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.
Overall Study
| Stage | AeroForm Tissue Expander |
|---|---|
| STARTED | 50 |
| COMPLETED | 48 |
| NOT COMPLETED | 2 |
Reasons for not completing this period:
| Reason | AeroForm Tissue Expander |
|---|---|
| Withdrawal by Subject | 2 |
Analysis population for the primary outcome, as defined in the registry: * of participants is 48: # treated (50) minus participant failed exchange of both breasts for non-device related reason (1) and participant not analyzed due to withdrawal (1). * of breasts is 80: # breasts treated (86) minus # breasts failed exchanged due to non-device related reason (4) and # breasts not analyzable due to withdrawal (2).
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: 50 Subjects treated under protocol
| Characteristic | Unit | AeroForm Tissue Expander |
|---|---|---|
| Participants analysed | 50 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 47 |
| Age, Categorical: >=65 years | Participants | 3 |
| Sex: Female, Male: Female | Participants | 50 |
| Sex: Female, Male: Male | Participants | 0 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 8 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 42 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| Race (NIH/OMB): Asian | Participants | 3 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 2 |
| Race (NIH/OMB): White | Participants | 40 |
| Race (NIH/OMB): More than one race | Participants | 1 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 4 |
| Region of Enrollment: United States | participants | 50 |
| Body Mass Index | lbs/in^2 | 24.5 (SD 3.57) |
6. Primary Endpoint
The registry lists the primary outcome as Number of Breasts With Successful Tissue Expansion With Exchange to a Permanent Breast Implant Unless Exchange is Precluded by a Non-device Related Event, measured over 6 months.
| Element | Registry entry |
|---|---|
| Result type | Count Of Units |
| Measure of spread | not applicable |
| Unit | breasts |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint counts breasts with successful tissue expansion followed by exchange to a permanent breast implant, unless exchange was precluded by a non-device-related event. The registry sets the assessment timeframe at 6 months. It explicitly counts breasts as failures when the expander is removed or replaced because of a device-related adverse event or device malfunction.
This endpoint is used to represent completion of a reconstruction-related process rather than a single measurement of expansion. It incorporates both reaching the point of exchange and the stated reasons for not reaching it. The exception for a non-device-related event distinguishes certain reasons exchange could not occur from device-related problems; however, the registry's full operational handling of every possible event is not reported.
The unit is breasts, and the endpoint is analyzed per breast. This matters because breast-level observations from one participant may be related to each other. A breast count therefore should not automatically be read as a count of participants. The registry reports 80 breasts in the primary analysis population, while the posted primary outcome value and its uncertainty are not reported in the registry record.
In general, a prespecified endpoint helps make clear which events qualify as success or failure before interpreting a result. Here, the description identifies the outcome and some failure rules, but the registry record does not report the observed count of successful breasts or a confidence interval. Without those results, the endpoint definition can be interpreted, but the frequency of success in this study cannot be assessed from the record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record provides the study design, the primary endpoint definition, and partial information about the analysis population, but it does not report the primary endpoint result. No number of successful breasts, corresponding proportion, or uncertainty interval is reported in the registry record. The central outcome question therefore cannot be answered from the posted record alone.
The available design information identifies this as a single-group study. Its data can describe what happened among breasts included in the analysis, but the design does not provide a randomized control group for estimating a comparative treatment effect. A count within one study group, even if it were reported, would not by itself show how the outcome would differ under another device, another reconstruction approach, or no use of this device. Those comparisons are not available from this record.
The unit of analysis also matters. The endpoint is a count per breast, while enrollment is given per participant. The primary analysis population is reported as 48 participants and 80 breasts. Breasts from the same participant may share characteristics and care experiences; in general, treating related observations as fully independent can make uncertainty appear narrower than it should. The record does not report whether or how any statistical method accounted for within-participant dependence.
The endpoint definition includes failures related to device adverse events or malfunction and an exception when exchange is precluded by a non-device-related event. That makes the classification rule important to interpretation. The registry describes some exclusions from the primary analysis population, including participant-level exclusions and breast-level exclusions, but the breast-level description is cut off. The complete disposition of all treated breasts and the reasons for each exclusion are not reported in the registry record.
The record lists a secondary outcome concerning the per-protocol cohort, but the result and the relationship between that analysis and the primary analysis are not reported. It also lists three analyses without describing their methods or whether they address different populations or hypotheses. Without these details, the extent to which the analyses could yield different findings cannot be evaluated.
Safety information is reported separately from the primary endpoint. The registry lists 11 participants with serious adverse events among 50 at risk, 8 participants with other adverse events among 50 at risk, and 0 deaths. These are descriptive registry figures; the record does not provide enough information to infer causation or to compare safety with another treatment group. Serious adverse-event terms and their reported percentages add context, but they do not substitute for the missing primary outcome result.
Overall, the posted information supports a description of the study's purpose and endpoint rules, but not an estimate of the observed primary outcome or its precision. Any conclusion about the endpoint frequency or a comparative effect would require information not reported in the registry record.
9. Statistical Methods Explained
The registry identifies the primary outcome as a count of breasts, with a success definition based on tissue expansion and exchange to a permanent breast implant. In general, a count endpoint records the number of units meeting a definition. It differs from a continuous endpoint, such as a measurement on a numeric scale, and from a time-to-event endpoint, which concerns the time until an event occurs. Here, the unit is a breast, and the timeframe is 6 months.
What does the count represent?
A count is meaningful only in relation to the population from which it was obtained and the rules used to classify each unit. The registry reports that 80 breasts were included in the primary analysis population. It says breasts removed or replaced because of a device-related adverse event or malfunction are counted as failures. It also describes an exception when exchange is precluded by a non-device-related event. The full accounting of the breast-level analysis population is not reported in the registry record, and neither is the observed count of successful breasts.
Counts may be analyzed with statistical methods designed for count data, but the suitable method depends on the data structure and scientific question. A simple count alone does not communicate uncertainty. In general, an interval estimate can show a range of values compatible with the observed data under the model used. A narrow interval indicates greater precision than a wide interval, but neither guarantees that the endpoint definition or analysis assumptions are appropriate. The registry does not report an interval estimate for the primary endpoint.
Why does the unit of analysis matter?
The study enrolled participants, but the primary endpoint is analyzed per breast. When a participant contributes more than one breast, observations may be correlated: for example, the same participant's health, care setting, or clinical decisions can affect both breasts. General statistical methods for clustered or correlated observations account for that dependence when estimating uncertainty. If dependence is ignored, standard errors and confidence intervals may not reflect the true precision. The registry record does not describe whether the analysis accounted for this issue.
In general, over-dispersion is a feature of count data in which observed variability is greater than a chosen statistical model expects. A model that fails to allow for over-dispersion can understate uncertainty. Whether over-dispersion is relevant depends on the distribution of the observed counts and the analysis method. Those details are not reported in the registry record, so no conclusion about over-dispersion or model fit is possible.
What can a single-group design estimate?
A single-group study can describe outcomes observed in its study population. A comparative effect requires a basis for comparing outcomes under different conditions. Random allocation can help make groups comparable on average, while a nonrandomized or single-group design leaves other explanations for observed outcomes harder to separate from the intervention. This study is listed as single group, with allocation NA and no masking. A randomized comparison is not reported. Thus the record does not support a randomized between-group treatment-effect estimate.
Masking is listed as NONE. In general, masking can reduce the influence of knowledge about treatment assignment on outcome assessment or other study processes, depending on what is masked. The record does not explain which people were unmasked or how that status affected endpoint classification. No further inference about the consequences of the masking status can be made from the registry description.
How should uncertainty be understood?
A confidence interval is a statistical summary of uncertainty around an estimate, calculated under specified assumptions. It is not a guarantee that the true value lies within the interval, nor does it capture every source of uncertainty, such as bias from selection or measurement. For this study, no primary endpoint estimate or confidence interval is reported in the registry record, so its precision cannot be assessed.
Statistical significance, if reported, would address a question defined by a statistical test and its assumptions; it would not by itself establish clinical importance. This registry record does not report a primary endpoint test or p-value. It also does not report the analysis plan, sample-size justification, or interim analyses. Those omissions prevent reconstruction of the planned inferential approach.
Planning calculations based on an observed effect are illustrations of what a later study might require under stated assumptions; they are not evidence that the present study had a particular probability of detecting an effect. Such calculations are not observed power. The registry's general planning description refers to a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effect fractions based on an observed effect. Those are described as planning assumptions, not as the trial's own design. This study itself is listed as single group, so an equal two-arm allocation does not describe its registered design.
In general, sample-size planning depends on the target effect, outcome variability, error rates, allocation, and analysis method. A planning illustration cannot establish that a study was adequately designed for its actual objective unless the assumptions and intended analysis align with that objective. The registry does not report the study's own sample-size justification or a detailed statistical plan, and no additional planning conclusion can be drawn from the available record.
Finally, the registry lists a per-protocol secondary outcome as well as the primary endpoint. Per-protocol analyses commonly focus on participants or units meeting specified adherence or eligibility rules, but the precise rules must be defined for a particular study. The rules and results for this secondary cohort are not reported in the registry record. Its findings therefore cannot be compared with the primary analysis or interpreted as a sensitivity analysis based on the available information.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary endpoint and a secondary outcome concerning successful tissue expansion with exchange to a permanent implant in the per-protocol cohort. It also lists three analyses, but their exact content, ordering, and relationship to the outcomes are not reported in the registry record. It is therefore not possible to determine whether the analyses address separate populations, repeated model specifications, or multiple hypotheses.
In general, testing multiple hypotheses can increase the chance of obtaining at least one apparently notable result by chance. A prespecified testing sequence or adjustment can address some multiplicity concerns, but the appropriate approach depends on the questions and analysis plan. The registry does not report whether any multiplicity adjustment or hierarchical testing strategy was planned. No conclusion about control of false-positive findings can be made.
The primary analysis population is described as 48 participants and 80 breasts. The record attributes participant-level exclusions to a participant who failed exchange of both breasts for a non-device-related reason and a participant who withdrew. It also states that four breasts were excluded because exchange failed for a non-device-related reason, but the remaining breast-level description is incomplete in the registry record. The full participant and breast disposition is not reported there.
Missing-data methods, imputation, and sensitivity analyses are not reported in the registry record. Withdrawal is mentioned, but the record does not explain how missing endpoint information was handled or whether the withdrawn participant contributed any data. It also does not report the amount or pattern of any other missing outcome information.
The primary endpoint is described for the analysis population, while a secondary outcome refers to a per-protocol cohort. The criteria for that cohort and the handling of deviations are not reported. Without these details, the influence of exclusions, missing data, or differences between analysis populations cannot be assessed.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| AeroForm Tissue Expander | 11 | 50 | 22.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| AeroForm Tissue Expander | 0 of 50 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| AeroForm Tissue Expander | 8 of 50 |
Most frequent serious adverse event terms
| Event term | Organ system | AeroForm Tissue Expander |
|---|---|---|
| cellulitis | Reproductive system and breast disorders | 4 of 50 |
| inflammation (red breast syndrome) | Reproductive system and breast disorders | 2 of 50 |
| wound dehiscence | Reproductive system and breast disorders | 1 of 50 |
| hematoma | Reproductive system and breast disorders | 1 of 50 |
| seroma | Reproductive system and breast disorders | 1 of 50 |
| neutropenic fever, weakness | Immune system disorders | 1 of 50 |
| urinary tract infection | Renal and urinary disorders | 1 of 50 |
Most frequent non-serious adverse event terms
| Event term | Organ system | AeroForm Tissue Expander |
|---|---|---|
| erythema | Skin and subcutaneous tissue disorders | 5 of 50 |
| seroma | Reproductive system and breast disorders | 3 of 50 |
Serious events with the highest arm-level rate: cellulitis (8.0%), inflammation (red breast syndrome) (4.0%), wound dehiscence (2.0%), hematoma (2.0%), seroma (2.0%).
The registry lists 11 participants with serious adverse events among 50 at risk in the AeroForm Tissue Expander group. It lists 8 participants with other adverse events among 50 at risk and reports 0 deaths. These are descriptive figures for the study group; they are not comparisons with a control group.
The serious adverse-event terms with reported percentages are cellulitis, 8.0%; inflammation (red breast syndrome), 4.0%; wound dehiscence, 2.0%; hematoma, 2.0%; seroma, 2.0%; and neutropenic fever, weakness, 2.0%. The registry does not provide further context for interpreting these terms, such as event timing or whether events were considered related to the device. The percentages should be read as reported, not as proof of causation.
In general, an adverse-event count describes events recorded under a study's reporting rules. A serious adverse event is a category of event severity; it is not itself proof that the study device caused the event. The registry figures also do not establish whether a participant experienced more than one event. Without a comparator group, the data cannot show how these figures differ from another treatment or from background risk.
12. What the Result Does, and Does Not, Mean
The record establishes that a single-group study evaluated the AeroForm Tissue Expander System for breast reconstruction, with a primary endpoint based on successful expansion and exchange to a permanent breast implant. It defines certain device-related events as failures and identifies a 6-month timeframe. These details clarify what the primary outcome was intended to measure.
However, the primary endpoint result is not reported in the registry record. There is no posted count of successful breasts, estimate of the success frequency, or uncertainty interval to interpret. It is therefore not possible to state how often the endpoint was achieved in the analyzed population or how precisely that frequency was estimated.
The design also limits what any single-group result could establish. Without a concurrent comparator and randomized allocation, an observed outcome could not by itself isolate the effect of the device from other factors. The registry's allocation field is NA, and the study is described as single group. It is not a like-for-like control comparison.
The analysis uses breasts as units, while the study enrollment is recorded in participants. Because a participant may contribute more than one breast, the observations may be related. The record does not explain how that dependence was handled statistically. It also gives only a partial account of exclusions from the primary analysis population and does not report missing-data methods or the detailed rules for the per-protocol secondary cohort.
The serious and other adverse-event figures offer descriptive safety information for the study group, along with a report of 0 deaths. They do not establish that events were caused by the device, and they do not provide a comparative safety estimate. In general, interpretation of safety requires attention to event definitions, follow-up, attribution, and the population assessed; several of those details are not reported in the registry record.
Accordingly, the record supports understanding the study's question, design, endpoint definition, and some safety counts. It does not support a conclusion about the observed primary outcome, a comparative treatment effect, or a causal safety effect. Those conclusions require results or analysis details that are not reported in the registry record.
13. Why This Trial Matters Statistically
This study illustrates why the definition and unit of an endpoint matter as much as its label. The primary outcome is not a participant-level response or a measurement of expansion alone; it is a breast-level count tied to successful expansion and exchange to a permanent implant, subject to stated rules for device-related failures and non-device-related barriers. Readers need those rules to know what the count represents.
The record also shows the distinction between enrollment and analysis population. Enrollment is reported as 50, while the primary analysis is described in terms of 48 participants and 80 breasts. This makes it important to follow how participants and outcome units enter an analysis rather than treating the enrollment figure as the denominator for every result. The record's incomplete breast-level accounting limits that assessment.
A second statistical lesson is that a single-group design answers a different question from a randomized comparison. It can describe outcomes in the enrolled study group, but it cannot directly estimate how those outcomes compare with a concurrent alternative. The absence of a reported primary result adds another limitation: endpoint definitions alone do not show the frequency of success or its precision.
Finally, the registry record leaves several analysis details unresolved, including how dependence between breasts was handled, how missing data were treated, and how the listed analyses relate to one another. Such details influence uncertainty and interpretation. The study is therefore useful for illustrating how design, outcome definition, analysis population, and reporting completeness jointly determine what can be learned from clinical trial results.
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.
The main limitation for interpreting efficacy is that the primary endpoint result is not reported in the registry record. The endpoint definition and timeframe are available, but there is no observed count of successful breasts or estimate of uncertainty. The posted record therefore does not permit a direct assessment of the primary outcome.
The study is listed as single group, with allocation NA and no masking. It does not include a randomized comparison in the registry record. As a result, the record cannot support a like-for-like estimate of the outcome under an alternative treatment. This limitation is distinct from statistical precision: even a precise single-group estimate would not, by itself, establish a comparative effect.
The primary endpoint is analyzed per breast, whereas enrollment is per participant. The record does not say whether the analysis accounted for correlation between breasts from the same participant. It reports 48 participants and 80 breasts in the primary population, but the breast-level explanation of exclusions is incomplete. It also does not report the complete endpoint disposition or the handling of missing outcome information.
The registry lists a per-protocol secondary outcome and three analyses, but the analysis methods, cohort rules, and relationship among analyses are not reported. No multiplicity approach, detailed statistical plan, sample-size justification, or interim analysis plan is reported. This prevents evaluation of whether the analyses followed a prespecified strategy or how uncertainty was calculated.
Safety information is descriptive and lacks a concurrent comparator in this record. The registry does not report further detail about timing, attribution, or repeated events. The recorded adverse-event counts should therefore not be interpreted as comparative rates or as evidence that an event was caused by the device.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: AirXpanders AeroForm Tissue Expander System for Breast Reconstruction — NCT02504424.
- Registry record last updated 2019-01-29; status last verified 2019-01.
- Results first posted 2018-09-05.
- 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.
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18. Record Summary
NCT02504424 is a completed, single-group study of the AeroForm Tissue Expander System for breast reconstruction, sponsored by AirXpanders, Inc. The registry reports enrollment of 50 and describes remote-control inflation with carbon dioxide. The primary endpoint counts breasts with successful tissue expansion and exchange to a permanent breast implant at 6 months, with specified device-related failures counted as unsuccessful.
The primary analysis population is described as 48 participants and 80 breasts, but the breast-level accounting is incomplete. The primary endpoint result, its uncertainty, and detailed statistical methods are not reported in the registry record. The record lists a per-protocol secondary outcome and three analyses without describing their methods or relationship.
Safety figures include 11 participants with serious adverse events among 50 at risk, 8 with other adverse events among 50 at risk, and 0 deaths. These are descriptive figures from a study without a comparator group and do not establish causation or comparative safety.