Surgical Treatment of Post-surgical Mastectomy Pain Utilizing the Regenerative Peripheral Nerve Interface: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Surgical Treatment of Post-surgical Mastectomy Pain Utilizing the Regenerative Peripheral Nerve Interface (NCT04530526), a na na study. The primary outcome is Change in Pain Level.

2. Clinical Question

3. Trial Design

This is a completed, single-group interventional study of the Regenerative Peripheral Nerve Interface procedure for Post-Mastectomy Chronic Pain Syndrome. The sponsor is University of Michigan Rogel Cancer Center. The registry records enrollment of 26 and lists the phase as NA. Allocation is also listed as NA, and masking is listed as NONE. These entries are consistent with the record's single-group designation: it does not describe random assignment or a masked comparison.

The study summary says the investigators planned to evaluate patient-reported post-mastectomy pain and intercostal neuromas after mastectomy. The intervention description refers to evaluative ultrasound measurements and a standard panel of patient-reported outcome measures addressing pain experience, anxiety, and depression. The listed primary outcome is Change in Pain Level, expressed as a mean score on a scale, with Standard Error as the dispersion measure. Its stated timeframe is baseline and 9 months post surgery.

The outcome description gives assessments at baseline, at the RPNI pre-operative visit approximately 3 months after enrollment, and approximately 3 and 9 months after surgery. It describes average study involvement as 12 months and notes that some patients could be followed until the study stopped. The actual follow-up achieved, and the amount of follow-up available for each assessment, are not reported in the registry record.

The registry lists a start date of 2019-07-12, primary completion on 2023-06-30, and status COMPLETED. It reports six outcome measures but zero analyses. It does not report a protocol-level statistical plan, a sample-size justification, or how the single-group design was to be handled analytically. These omissions matter because a completed status does not itself provide outcome estimates or establish that every planned assessment was reported.

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

Reasons for not completing this period:

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 Pain Level, measured over baseline, and 9 months post surgery.

The primary endpoint is titled Change in Pain Level. It is a continuous outcome summarized as a mean score, with Standard Error identified as the measure of dispersion. The stated primary timeframe compares baseline with 9 months post surgery. The registry describes validated patient-reported outcome surveys, including the Numerical Pain Rating Scale, Short Form McGill Pain Questionnaire 2, Pain Catastrophizing Score, PROMIS Intensity, PROMIS Interference, and PROMIS Neuropathic.

The scales use different ranges and represent related but distinct dimensions of pain. The record states that higher scores indicate more pain for each listed scale: 0-10 for the Numerical Pain Rating Scale and Short Form McGill Pain Questionnaire 2, 0-52 for Pain Catastrophizing Score, 0-12 for PROMIS Intensity, 0-24 for PROMIS Interference, and 0-20 for PROMIS Neuropathic. A score change is therefore interpreted within its own scale; the scales should not be treated as interchangeable units.

Patient-reported measures can capture a person's reported pain experience and its effects, which may not be represented by a clinical examination alone. The registry's outcome description includes additional assessment times, while the primary timeframe specifically names baseline and 9 months post surgery. It does not report the observed means, changes, or uncertainty for any of these measures. The choice of scale and assessment schedule can be described, but the magnitude and precision of the endpoint result cannot be evaluated from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a mean of a continuous measure and names Standard Error as the dispersion statistic. These terms describe how an outcome might be summarized; they are not themselves a reported result. No outcome mean, change estimate, or Standard Error is posted in the registry record.

What a mean and Standard Error describe

In general, a mean is the arithmetic average of the observed scores included in an analysis. It summarizes the center of those scores, but does not show how widely individual scores vary. Standard Error describes the uncertainty in an estimated mean under the assumptions of the analysis. It is not a direct description of the spread of individual patient scores. A standard deviation, distribution plot, or other description of patient-level variability would answer a different question. The registry does not report those details for the primary endpoint.

The outcome is described as a change between baseline and 9 months post surgery. In general, an analysis of change can be based on each participant's paired observations, or it can compare group summaries at separate timepoints. These approaches can differ, particularly if different participants contribute data at each visit. The registry record does not state how change was calculated, which observations were included, or whether a model was used to account for repeated assessments. No method should be assumed from the outcome title alone.

Repeated assessments and the outcome scales

The registry describes assessments at baseline, at the RPNI pre-operative visit approximately 3 months after enrollment, and approximately 3 and 9 months after surgery. Repeated measurements on the same participants are generally correlated: a person's score at one visit may be related to that person's score at another. General statistical methods can account for that dependence when estimating change across time. The analysis method used in this study is not reported in the registry record.

The named measures do not all have the same range. In the registry description, the Numerical Pain Rating Scale and Short Form McGill Pain Questionnaire 2 range from 0-10, Pain Catastrophizing Score from 0-52, PROMIS Intensity from 0-12, PROMIS Interference from 0-24, and PROMIS Neuropathic from 0-20. Higher scores are described as indicating more pain. An average change remains tied to the scale on which it was measured; comparing raw changes across scales without considering their different ranges and content can mislead. The record does not identify a common transformed metric or a rule for combining these measures.

Uncertainty and interpretation

In general, a confidence interval gives a range of estimates compatible with the data and the assumptions of the method. Its width conveys precision: wider intervals indicate greater uncertainty than narrower intervals. A p-value addresses how compatible the data are with a specified statistical model or null hypothesis; it does not measure the size or clinical importance of an effect. Neither a confidence interval nor a p-value for the primary endpoint is reported in the registry record. Without an estimate and an uncertainty measure, precision cannot be judged.

Over-dispersion is a general issue when observed variability exceeds what a model assumes. If present and not handled appropriately, it can make uncertainty estimates unreliable. The posted endpoint is continuous and the record gives no model specification or dispersion diagnostics, so there is no basis to say that over-dispersion was assessed or affected this analysis. More broadly, the registry does not report distributional checks, model assumptions, covariate adjustment, or sensitivity analyses.

Design and planning calculations

The study is recorded as single-group, with allocation listed as NA. A planning illustration based on an observed effect is described using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. Such an illustration is a planning calculation, not an observed trial result and not observed power. Its equal-allocation, two-arm assumptions do not describe the recorded single-group design. The registry does not report the study's own sample-size justification or statistical plan, so the illustration should not be treated as evidence of the rationale used to enroll participants.

In general, a planning sample size depends on the target effect, variability, analysis, and chosen error rates. An illustration based on an observed effect is especially dependent on that effect estimate and its uncertainty. It cannot establish that a study had adequate precision for its actual design or outcomes. No power calculation for the trial's single-group analyses is reported in the registry record.

What is missing from the analysis record

The record reports zero analyses. It does not provide the analysis population, the number of participants contributing to each assessment, the handling of missing observations, or whether the analysis followed a prespecified plan. It also does not describe multiplicity handling for the named outcome measures. Because these are absent, the analysis method, assumptions, and robustness of any result cannot be independently evaluated from the registry record. General statistical principles can explain what these choices mean, but cannot fill in methods that are not reported.

10. Multiplicity, Missing Data and Analysis Populations

The registry names six outcome measures and describes several assessment times, while identifying Change in Pain Level as the primary outcome. The record does not report a hierarchy among the individual scales, specify which scale or scales constitute the primary analysis, or state how multiple comparisons were handled. When several outcomes or timepoints are examined, the chance of at least one apparently notable result can increase. General approaches to multiplicity include prespecifying a primary comparison, adjusting inference, or treating secondary analyses as exploratory. The registry does not say which approach, if any, was used.

Missing-data handling is also not reported in the registry record. It does not state how many participants completed each visit, why assessments might be absent, whether analysis required observations at both baseline and follow-up, or whether imputation or another method was used. In general, conclusions from longitudinal outcomes can depend on why data are missing and on the assumptions used to address them. Without those details, the extent to which missing observations could influence a change estimate cannot be assessed.

The analysis population is not reported in the registry record. It is therefore unclear whether analyses were intended to include all enrolled participants, only those who received surgery, or only those with particular follow-up data. The record also does not describe exclusions, protocol deviations, or sensitivity analyses. These omissions leave the link between the recorded enrollment and any potential outcome estimate unspecified. Since no analyses or numerical outcome results are posted, none of these analysis choices can be verified against reported findings.

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

The record establishes that a completed single-group study was registered to evaluate RPNI surgery in patients with post-mastectomy chronic pain. It specifies a primary pain outcome, lists six patient-reported measures, and describes assessment from baseline through follow-up after surgery. It also records enrollment of 26. These registry entries characterize the study's intended question and basic design; they do not provide an estimate of how scores changed.

The record does not report the results needed to determine the observed direction or size of change, or how precise an estimate might be. It therefore cannot establish from the posted results whether the pain scores increased, decreased, or remained similar. It also cannot support a conclusion about whether any change was clinically meaningful, because no outcome estimates or thresholds for clinical importance are reported.

Even if a before-and-after change were available, a single-group design would not provide a concurrent treatment comparison. In general, observed changes over time can reflect more than the intervention under study. The registry record does not describe a control group or a randomized comparison that would allow those alternative explanations to be evaluated directly. The information cannot be used to infer a comparative effect against another procedure or against standard care.

The registry lists zeros for the at-risk and affected counts in its adverse-event group, including deaths. These entries should be read as registry fields, not as proof that no harms occurred: the at-risk count is also recorded as zero, and the record does not provide further context for these values. The entries do not permit a complete assessment of safety or the frequency of adverse events.

In short, the record describes an evaluation and its intended measures, but does not report the primary outcome analyses. It cannot establish the size, precision, clinical importance, or causal interpretation of a pain change, nor can it support a treatment recommendation.

12. Why This Trial Matters Statistically

This trial is statistically notable because it addresses a patient-reported outcome in a single-group design. Pain is measured using several named scales, each covering a specific aspect of the reported experience and using its own score range. The registry also describes repeated assessment before and after surgery. These features make clear why outcome definitions, timing, and the analysis population matter when interpreting changes over time.

A single-group study can describe participants' scores across assessments, but it does not include a concurrent control group in the registry record. General statistical interpretation must therefore distinguish observed change from a treatment effect attributable to the procedure. That distinction is important even when a study has a stated clinical objective and a defined follow-up schedule.

The record also illustrates the difference between study completion and result reporting. It marks the study COMPLETED and records enrollment of 26, yet reports zero analyses and no numerical primary outcome results. Without estimates and uncertainty measures, readers cannot judge effect magnitude or precision. A status label and a measurement plan do not substitute for analysis results.

Finally, the absence of reported details about multiplicity, missing assessments, and analysis populations limits assessment of how the outcome data would support a conclusion. These are not merely technical footnotes: with multiple measures and repeated visits, they affect which observations and comparisons a result represents. The record makes the intended evaluation understandable, while leaving the statistical evidence needed to interpret its outcome unavailable.

13. 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 most immediate limitation of the registry record is that it contains no numerical outcome results or analyses. Although the study is marked completed, there are no posted mean scores, change estimates, uncertainty measures, or inferential results for the primary endpoint. Consequently, the planned assessment cannot be evaluated for observed magnitude, direction, or precision.

The single-group design has no concurrent control group listed. Any before-and-after change, if reported elsewhere, would not alone distinguish the procedure's contribution from other changes over time. The registry does not report a comparator, random allocation, or a method to address that limitation analytically.

The outcome description includes six patient-reported measures with different score ranges and several assessment times. The record does not clarify how those measures were prioritized or how multiple comparisons were handled. It also does not report which assessment timepoints were completed for which participants, or how missing observations were addressed. The analysis population and treatment of deviations are not specified.

Details needed to assess the intervention and outcome collection are limited. The registry does not report operative characteristics, adherence, the enrolled participants' baseline profile, or the results of evaluative ultrasound measurements. It does not provide the protocol-level statistical plan, sample-size justification, or outcome-analysis method. The adverse-event fields list zeros for at-risk and affected counts, including deaths, but provide no context that would establish the completeness of safety reporting. These limitations concern what can be learned from the registry record and should not be mistaken for evidence that an unreported analysis or assessment did not occur.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: Surgical Treatment of Post-surgical Mastectomy Pain Utilizing the Regenerative Peripheral Nerve Interface — NCT04530526.
• Registry record last updated 2025-12-24; status last verified 2025-12.
• Results first posted 2025-12-24.
• 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.

17. Record Summary

The registry record identifies NCT04530526 as a completed single-group study titled Surgical Treatment of Post-surgical Mastectomy Pain Utilizing the Regenerative Peripheral Nerve Interface. University of Michigan Rogel Cancer Center is listed as sponsor. The condition is Post-Mastectomy Chronic Pain Syndrome, and the intervention is the Regenerative Peripheral Nerve Interface procedure. Enrollment is recorded as 26; phase and allocation are listed as NA, and masking is NONE.

The primary outcome is Change in Pain Level, summarized as a mean score with Standard Error, with a stated timeframe of baseline and 9 months post surgery. Six patient-reported outcome measures are named. The record lists a study start date of 2019-07-12, primary completion on 2023-06-30, and status COMPLETED. It reports zero analyses and does not report numerical outcome results, missing-data methods, or the analysis population.