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 A Phase II Study of 131I- Metaiodobenzylguanidine (MIBG) for Treatment of Metastatic or Unresectable Pheochromocytoma and Related Tumors (NCT01413503), a na phase 2 study. The primary outcome is Number of Patients With Complete (CR), Partial (PR), or Minor (MR) Response and Without Progressive Disease.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01413503 |
| Phase | Phase 2 |
| Condition | Pheochromocytoma, Paraganglioma |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 50 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of California, San Francisco |
| Results posted | Yes |
2. Clinical Question
Population
Patients with metastatic or unresectable pheochromocytoma and related tumors. The listed conditions are pheochromocytoma and paraganglioma; the registry record does not provide additional eligibility details in the population description.
Intervention
131I-MIBG, administered by intravenous infusion. The arm description specifies a dose of 8-12 mCi/kg, with a maximum of 500 mCi ± 10% at the investigator's discretion.
Comparator
There was one study group and no comparator arm. Allocation is listed as NA, so the study does not provide a randomized or concurrent control comparison.
Primary question
How many participants had a complete, partial, or minor response and were without progressive disease one year after initial treatment? The registry record does not report the result for this endpoint.
The clinical question is therefore framed around a count of participants meeting a combined response-and-disease-status criterion at a specified follow-up time. It is not a comparison of response rates between 131I-MIBG and another treatment. The record describes the study as a prospective Phase II evaluation, but its single-group design means the posted endpoint, even if its result were available, would describe outcomes among the treated group rather than isolate the effect of treatment from other explanations.
The endpoint combines several response categories—complete, partial, or minor response—with the requirement that progressive disease be absent. Its definitions draw on measurable soft tissue disease, bone lesions, and, for complete response, biochemical markers. The registry description gives criteria for these categories, but does not provide participant-level data or explain how participants with different patterns of disease were classified.
3. Trial Design
This is a Phase II, prospective, single-group study sponsored by the University of California, San Francisco. The registry lists the study as completed, with enrollment of 50. Its start is recorded as 1991-05, and its primary completion date is 2007-09-06. These record fields describe the trial's status and dates; they do not establish when each participant was enrolled or followed.
There is one intervention group, 131I-MIBG, and allocation is listed as NA. Masking is listed as none. No control group or randomized comparison is described. Consequently, the design can describe outcomes observed in the study group, but cannot directly compare those outcomes with an untreated group or a group receiving another intervention.
The intervention description states that 131I-MIBG was diluted in 25 ml of normal saline and infused intravenously through a peripheral or central line over 120 minutes. The stated dose was 8-12 mCi/kg, with a maximum of 500 mCi ± 10% at the investigator's discretion. The record does not report additional treatment schedules or protocol details beyond this description.
The primary endpoint is a participant count assessed after 1 year from initial treatment. It includes participants with complete, partial, or minor response and without progressive disease. The registry lists one outcome measure, but no analysis records. It does not report the observed count for the primary endpoint, an effect estimate, or a confidence interval. The study's sample-size justification, statistical analysis plan, interim analyses, and detailed analysis population are not reported in the registry record.
As a single-group Phase II study, the design is suited to documenting outcomes within the treated cohort. It does not by itself support a treatment-versus-control effect estimate. Any interpretation should keep that design distinction in view, alongside the absence of a posted primary endpoint result.
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 | 131I-MIBG |
|---|---|
| STARTED | 50 |
| COMPLETED | 49 |
| NOT COMPLETED | 1 |
Reasons for not completing this period:
| Reason | 131I-MIBG |
|---|---|
| Lost to Follow-up | 1 |
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: number of evaluable participants
| Characteristic | Unit | 131I-MIBG |
|---|---|---|
| Participants analysed | 49 | |
| Age, Continuous | years | 42.6 (10.3 to 64.4) |
| Sex: Female, Male: Female | Participants | 20 |
| Sex: Female, Male: Male | Participants | 29 |
| Region of Enrollment: United States | participants | 49 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Patients With Complete (CR), Partial (PR), or Minor (MR) Response and Without Progressive Disease, measured over After 1 year from initial treatment.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants who had a complete (CR), partial (PR), or minor (MR) response and were without progressive disease after 1 year from initial treatment. This is a count endpoint rather than a time-to-event measure or a comparison between treatment groups. The registry record lists the endpoint but does not report how many participants met it.
The criteria combine disease status and response. For measurable soft tissue tumors, complete response is defined as no primary or metastatic tumor, together with normal catecholamines, metanephrines, and chromogranin A. Partial response is described using reductions in primary and measurable sites, positive bone sites, or bone marrow tumor. Minor response requires no new lesions, more than 50% reduction of any measurable lesion, and less than 25% increase in any existing lesion. These are the registry's stated definitions.
A response endpoint can provide a structured way to describe tumor changes at a defined follow-up point. Combining response with the absence of progressive disease makes the endpoint a composite of several clinical and measurement criteria. In general, such endpoints require consistent assessment rules because classification can depend on which types of lesions and markers are measurable. The registry record does not report further details about assessment procedures, adjudication, or handling of participants whose status at the assessment time was unknown.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies a primary response endpoint and a one-year assessment time, but does not report the endpoint result. It therefore does not establish how many participants met the combined response and no-progression criterion. No primary effect estimate, confidence interval, or p-value is reported in the registry record. Without those results, the endpoint's magnitude and statistical precision cannot be described.
The study has one group and no comparator. Any outcome count from such a design would describe the cohort observed; it would not, on its own, distinguish the effect of 131I-MIBG from the natural course of disease, other care, differences in patient characteristics, or measurement variation. This is a general limitation of single-group studies, not a claim about what occurred in this study.
The listed enrollment is 50, while the safety group reports 49 participants at risk for serious and other adverse events. The registry does not explain the difference between these figures. They should not be treated as interchangeable denominators: the enrollment field and safety risk set refer to different record entries, and the record does not say why one participant is absent from the safety denominator.
The registry lists six participants affected by serious adverse events among 49 at risk, 43 affected by other adverse events among 49 at risk, and four deaths. These are descriptive safety figures. The record does not identify whether the deaths were related to treatment, or whether the serious and other event categories overlap. Serious-event terms and percentages are also listed, but they do not replace a complete account of each participant's event history.
The record includes no analysis records. That means no analysis results are posted in the registry entry; it does not establish that no analyses were performed during the study. Statistical methods for the primary endpoint, missing-data handling, and analysis populations are not reported in the registry record. Without these details and the actual endpoint result, readers cannot evaluate the precision, robustness, or potential sensitivity of the efficacy analysis.
Planning illustrations use assumptions described as two-sided significance level 0.05, equal allocation between two arms, and a normal approximation, with effects set as fractions of the observed effect. They are planning calculations, not observed power. Their two-arm framing does not match the single-group trial design, and the registry entry does not report the endpoint result needed to interpret an observed-effect basis. Such illustrations should not be mistaken for evidence that the study was powered to detect a particular clinical effect.
9. Statistical Methods Explained
Statistical methods describe how observations are converted into estimates and how uncertainty is assessed. For this study, the registry record identifies a participant-count endpoint and a single study group, but does not report an analysis record or the statistical analysis plan. The following concepts are general explanations; they are not claims about methods used by the investigators.
What does a participant count describe?
A count reports how many people met a specified outcome definition. Here, the listed endpoint counts participants who had a complete, partial, or minor response and were without progressive disease at the stated one-year time point. A count can be informative about the observed cohort, but its interpretation depends on the denominator, the completeness of assessment, and consistent application of the response criteria. The registry does not report the count or a denominator for this primary endpoint.
Counts are different from comparisons. In a randomized trial, a comparison between groups can estimate how outcomes differ under the assigned interventions, subject to the study's design and analysis. In a single-group study, there is no concurrent control group against which to make that contrast. A count from the treated group alone cannot separate treatment effects from other influences on outcome. This is why the design is central to interpretation, not merely a background description.
What does a confidence interval add?
In general, a confidence interval describes the statistical uncertainty around an estimated quantity under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval for that estimate; neither width nor location alone resolves potential bias or the lack of a control group. No confidence interval for the primary endpoint is reported in the registry record, so its statistical precision cannot be assessed from the registry entry.
A p-value, when reported, addresses how compatible the observed data are with a specified statistical null model, under the assumptions of the test. It is not a measure of clinical importance and does not establish causation. The registry record does not report a p-value or specify a primary endpoint test. It would not be appropriate to infer statistical significance or a testing procedure from the study's Phase II designation.
How should the response definition be understood?
The primary endpoint combines response categories and absence of progressive disease at a fixed assessment time. The stated response definitions refer to tumor status, changes in measurable lesions, bone sites, bone marrow tumor, and biochemical markers. In general, a composite definition can capture more than one aspect of disease status, but it also means that the overall count depends on each component's operational rules. The registry gives the category definitions, but does not report how measurements were obtained, how ambiguous cases were resolved, or whether assessments were reviewed independently.
The endpoint is not described as a time-to-event outcome. It focuses on status at one year after initial treatment. In general, a fixed-time endpoint requires a method for addressing participants without an assessment at that time. The registry record does not report the number with missing assessments, how missing outcomes were handled, or whether the primary analysis included all enrolled participants or a subset.
What do the planning assumptions mean?
The planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. These are calculation assumptions, not evidence that participants were assigned to two arms. This study is listed as single-group with no comparator, so the illustration's two-arm framework is distinct from the trial's recorded design.
In general, sample-size planning asks how many observations might be needed to detect a specified effect under chosen assumptions. The answer depends on the assumed effect, variability, error rate, allocation, and analysis. A planning illustration does not show that an actual trial had a particular probability of detecting an effect, and it is not observed power. The registry record does not report the trial's own sample-size justification. It also does not report the primary outcome result that would allow a reader to assess what an observed-effect-based illustration represents.
Why do analysis populations matter?
In general, an analysis population specifies which participants contribute to a particular estimate. Choices can affect interpretation if some participants are excluded or lack outcome data. A study may define different populations for efficacy and safety, but the registry entry does not describe the primary efficacy analysis population. It lists 50 for enrollment and 49 at risk in the safety group; the reason for this difference is not reported. The safety denominator should not be assumed to be the efficacy denominator.
Interpretation therefore rests on a limited statistical record: the endpoint definition, its timing, the single-group design, and the safety summaries. The absent primary result, confidence interval, analysis plan, and missing-data description prevent a fuller assessment of the efficacy analysis and its uncertainty.
10. Exact Estimates for Each Arm
No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.
| Arm | Participants | Events | Observed % | Clopper-Pearson 95% CI | Wilson 95% CI | Bayesian 95% credible interval |
|---|---|---|---|---|---|---|
| 131I-MIBG | 49 | 28 | 57.1% | 42.2% to 71.2% | 43.3% to 70.0% | 43.2% to 70.0% |
R code and output
arm <- c("131I-MIBG")
n <- c(49)
events <- c(28)
for (i in seq_along(n)) {
ci <- binom.test(events[i], n[i])$conf.int # Clopper-Pearson exact interval
cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i]) # Bayesian, uniform Beta(1,1) prior
wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}
ARM 131I-MIBG 49 28 57.1 42.2 71.2 43.3 70.0 43.2 70.011. Multiplicity, Missing Data and Analysis Populations
The registry lists one outcome measure and zero analysis records. The one listed measure is the primary count of participants with complete, partial, or minor response and without progressive disease after 1 year from initial treatment. Its result is not reported in the registry record. The absence of posted analyses means the entry does not provide an analysis result; it does not establish whether analyses were conducted elsewhere or during the trial.
Multiplicity refers, in general, to the increased chance of false-positive findings when several hypotheses or outcomes are tested. Researchers may address it through prespecified testing strategies or other adjustments. The registry does not report a multiplicity plan, whether additional outcomes were analyzed, or whether any adjustment was used. With no posted analysis results or statistical plan, the approach to multiple testing cannot be assessed.
Missing-data methods matter when participants lack an outcome assessment or when measurements are incomplete. In general, different assumptions about missing outcomes can lead to different estimates. The registry record does not report how many participants had an unknown one-year response status, how missing endpoint data were handled, or whether sensitivity analyses were performed. It also does not describe the primary efficacy analysis population.
The safety group lists 49 participants at risk, compared with enrollment of 50. The reason for the difference is not reported. The record does not establish whether the difference reflects missing data, eligibility, timing, or another factor, so no explanation should be inferred. The efficacy denominator is not reported either. These omissions limit assessment of how completely the primary outcome was observed and which participants contributed to any analysis.
12. 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 |
|---|---|---|---|
| 131I-MIBG | 6 | 49 | 12.2% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| 131I-MIBG | 4 of 49 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| 131I-MIBG | 43 of 49 |
Most frequent serious adverse event terms
| Event term | Organ system | 131I-MIBG |
|---|---|---|
| Bronchiolitis obliterans organizing pneumonia | Respiratory, thoracic and mediastinal disorders | 2 of 49 |
| Myelodysplastic syndrome | Blood and lymphatic system disorders | 2 of 49 |
| Acute respiratory distress syndrome | Respiratory, thoracic and mediastinal disorders | 2 of 49 |
| Pulmonary Embolism | Vascular disorders | 1 of 49 |
Most frequent non-serious adverse event terms
| Event term | Organ system | 131I-MIBG |
|---|---|---|
| Neutropenia | Blood and lymphatic system disorders | 43 of 49 |
| Thrombocytopenia | Blood and lymphatic system disorders | 41 of 49 |
| Febrile neutropenia | Infections and infestations | 7 of 49 |
| Acute hypertension | Vascular disorders | 7 of 49 |
| Hypogonadism | Reproductive system and breast disorders | 4 of 49 |
| Hyperthyroidism | Endocrine disorders | 3 of 49 |
| Infection | Infections and infestations | 2 of 49 |
| Pulmonary embolism | Respiratory, thoracic and mediastinal disorders | 1 of 49 |
Serious events with the highest arm-level rate: bronchiolitis obliterans organizing pneumonia (4.1%), myelodysplastic syndrome (4.1%), acute respiratory distress syndrome (4.1%), pulmonary embolism (2.0%).
The safety summary lists 49 participants at risk for serious adverse events, with 6 affected, and 49 at risk for other adverse events, with 43 affected. It also lists 4 deaths. These are counts associated with the 131I-MIBG group; the registry record does not state that every event was caused by treatment. A death count alone does not establish cause or treatment relationship.
The listed serious adverse-event terms and percentages are bronchiolitis obliterans organizing pneumonia, 4.1%; myelodysplastic syndrome, 4.1%; acute respiratory distress syndrome, 4.1%; and pulmonary embolism, 2.0%. These figures should be read as the registry's reported term-level summaries. The entry does not provide further event-level detail, such as timing, duration, severity beyond the serious classification, or relationship to treatment.
The counts for serious and other adverse events should not be added or assumed to represent separate groups of participants. The registry does not say whether a participant could appear in both categories or whether the listed term percentages correspond to distinct participants or events. The difference between the enrollment figure of 50 and the safety risk set of 49 is also not explained. These safety summaries are descriptive and do not provide a comparison with another treatment group.
13. What the Result Does, and Does Not, Mean
The registry record describes a Phase II study of 131I-MIBG in a single group of patients with metastatic or unresectable pheochromocytoma and related tumors. It specifies an endpoint based on response and absence of progressive disease after 1 year from initial treatment. However, it does not report the number of participants who met that endpoint. As a result, the posted record does not show the observed primary outcome or its precision.
Even if a one-group response count were available, it would describe outcomes in the study cohort rather than provide a controlled estimate of treatment effect. Without a comparator, the study cannot directly show how those outcomes differ from what would have occurred under another treatment or without the intervention. This is a general limitation of single-group designs; it does not imply a particular outcome for this cohort.
The record also reports safety counts and term-level serious-event percentages. These provide descriptive information, but do not establish that events were caused by 131I-MIBG. No treatment relationship for deaths is reported. The safety summary does not include a control group, and it does not explain whether event categories overlap.
The endpoint definitions and intervention details help clarify what the study set out to assess. They do not substitute for the missing outcome result, analysis methods, or missing-data information. The registry record also does not report the sample-size justification or a statistical analysis plan. Planning illustrations based on assumptions should not be interpreted as observed power or as evidence of the actual trial's design, which is listed as single-group.
Accordingly, the record supports a description of the study design, planned endpoint, intervention, and posted safety summaries. It does not support a conclusion about the primary response result, its statistical uncertainty, or a causal treatment effect.
14. Why This Trial Matters Statistically
This study illustrates why a trial's design and its posted results must be read together. The registry describes a prospective Phase II evaluation with one intervention group and a response endpoint measured after 1 year. The endpoint is clinically interpretable as a count of participants meeting specified response and disease-status criteria, but the registry does not report the count. A defined endpoint without its result cannot answer how the cohort performed on that measure.
The single-group design also sets an important boundary on statistical interpretation. A study can document outcomes in a treated cohort, but without a comparator it cannot directly estimate how outcomes differ from those under another condition. That distinction remains even when response criteria are detailed or follow-up timing is specified.
The entry also shows the importance of denominators and analysis populations. Enrollment is listed as 50, while the safety group has 49 participants at risk. The record does not explain the difference, and it does not report the denominator for the primary endpoint. Readers therefore cannot determine from the registry entry how many enrolled participants contributed to efficacy assessment or why the safety risk set differs.
Finally, the record's lack of analysis results and statistical details limits evaluation of uncertainty, missing outcomes, and multiplicity. These are not minor presentation issues: they determine what can be inferred from a result and how robust that inference may be. The study is statistically informative as an example of how a registry entry can state a research question and intervention while leaving the central efficacy finding and analysis approach unreported.
15. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The primary limitation for interpreting efficacy is that the registry record does not report the result for its one listed primary outcome. No endpoint count, effect estimate, confidence interval, or p-value is reported. The entry therefore does not allow assessment of the observed response frequency or its statistical precision.
The study is listed as single-group, with allocation NA and no masking. No control group is described, so the design does not provide a concurrent treatment comparison. This restricts causal interpretation of any cohort outcome. The registry's brief summary describes an efficacy evaluation, but the record does not provide an analysis result that could be assessed.
Other important details are not reported in the registry record: the sample-size justification, statistical analysis plan, interim analyses, analysis population, missing-data handling, and procedures for response assessment or adjudication. The record also does not explain why enrollment is 50 while the safety group lists 49 at risk. These gaps prevent assessment of the completeness of outcome ascertainment and the rationale for the analysis approach.
The response definition includes several disease measurements and biochemical markers, but the entry does not report participant-level results or details of how each criterion was applied. Safety summaries are also limited: the record lists affected counts, deaths, and serious-event terms, but does not establish treatment relationships or explain overlap among categories. The registry entry should therefore be read as a limited account of design and descriptive safety information, not as a complete statistical report of the trial.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: A Phase II Study of 131I- Metaiodobenzylguanidine (MIBG) for Treatment of Metastatic or Unresectable Pheochromocytoma and Related Tumors — NCT01413503.
- Registry record last updated 2018-09-18; status last verified 2017-12.
- Results first posted 2018-09-18.
- 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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Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
19. Record Summary
NCT01413503 is a completed Phase II, prospective, single-group study sponsored by the University of California, San Francisco. It evaluates 131I-MIBG in patients with metastatic or unresectable pheochromocytoma and related tumors. The registry lists enrollment of 50, a start of 1991-05, and a primary completion date of 2007-09-06.
The intervention was administered intravenously at 8-12 mCi/kg, with a maximum of 500 mCi ± 10% at investigator discretion. The primary endpoint counts participants with complete, partial, or minor response and without progressive disease after 1 year from initial treatment. The endpoint result and analysis are not reported in the registry record.
The safety group lists 49 at risk, 6 affected by serious adverse events, 43 affected by other adverse events, and 4 deaths. The record does not report treatment relationships or explain the difference between the enrollment and safety counts.