Single Fraction High-Gradient Partial Breast Irradiation in Treating Patients With Low-Risk Stage 0-I Breast Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Single Fraction High-Gradient Partial Breast Irradiation in Treating Patients With Low-Risk Stage 0-I Breast Cancer (NCT02076074), a na na study. The primary outcome is Percentage of Patients Who Are Free of Serious Treatment Related Toxicity.

2. Clinical Question

The clinical question has two related parts. First, the study evaluates safety after delivering partial-breast radiation in a single session rather than across multiple treatments. Second, its stated purpose includes evaluating how well the approach works in low-risk stage 0-I breast cancer. The primary endpoint addresses the safety part: it is based on serious treatment-related toxicity, not on a direct comparison of cancer outcomes between treatment strategies.

The registry also lists outcomes concerning regional lymph nodes, distant metastases, quality of life, pain and cosmetic measures. Results for those outcomes are not reported in the registry record. Because there is no control group, the study cannot by itself establish how outcomes compare with another radiation schedule or with another treatment approach. Its findings must be understood as observations within the treated group.

3. Trial Design

The registry describes a completed, single-group study sponsored by Washington University School of Medicine. Enrollment was 50. The study began on 2014-04-02, and primary completion was recorded as 2023-05-18. The registry classifies allocation as NA, masking as NONE and the model as SINGLE GROUP. The phase field is NA, although the brief summary describes the study as phase I/II.

Participants in the treatment group underwent single-fraction high-gradient partial-breast irradiation within 8 weeks after partial mastectomy. The intervention is also named accelerated partial-breast irradiation. The registry’s description frames the treatment as radiation focused on the part of the breast containing cancer, rather than whole-breast radiation. Further treatment-delivery details, including dose and technical parameters, are not reported in the registry record.

The primary outcome concerns freedom from serious treatment-related toxicity, assessed up to 5 years. The registry defines acute toxicity as occurring from treatment start until day 90, and late toxicity as occurring from Day 91 until completion of 5 year follow-up. The study’s listed secondary outcomes include cancer status in regional lymph nodes and distant metastases, quality-of-life measures, pain, and cosmetic assessments. Their results are not reported in the registry record.

With a single group and no masking, the design is descriptive for the observed treated participants. There is no concurrent control group against which to separate treatment-associated outcomes from outcomes that might also occur because of the underlying disease, prior surgery, other care, or chance. The registry record does not report a detailed statistical analysis plan, a sample-size justification, interim analyses, or the methods used to handle follow-up and missing observations.

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

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 Percentage of Patients Who Are Free of Serious Treatment Related Toxicity, measured over Up to 5 years.

The primary endpoint is the percentage of patients who are free of serious treatment-related toxicity during follow-up up to 5 years. The registry describes this endpoint through the rate of acute and late treatment-related grade 3 or higher toxicity under CTCAE, v.4.0, or any other grade 4 or 5 toxicity attributed to the therapy. Listed concerns include breast pain, delayed wound healing, persistent seroma fluid accumulation, breast fibrosis and fat necrosis in the treated breast. Rare toxicities named in the record include radiation pneumonitis and pericarditis.

This endpoint is used to assess serious harms associated with the treatment, rather than to measure tumor control or compare treatment schedules. Distinguishing acute from late toxicity matters because treatment effects may arise at different times during follow-up. The registry defines the acute period as treatment start through day 90, and the late period as Day 91 through completion of 5 year follow-up.

The posted safety counts show zero participants affected by serious events among 50 at risk in both the acute and late groups. However, the registry record does not report a separate primary-endpoint estimate with a confidence interval, nor does it provide participant-level timing or attribution details. The counts should therefore be read as the recorded safety figures, not as a complete account of all possible toxicity or as a comparative estimate against another treatment.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods help distinguish what the observed data describe from what can be inferred beyond the participants who were followed. For this single-group study, the central descriptive quantities are counts of participants recorded with events and counts at risk. These summarize the registry’s entries for the treatment group, but they do not create a comparison with a different treatment or a control group.

What does a participant count describe?

A participant count records how many people in a specified group were identified with an outcome under the registry’s definitions. It is not automatically the same as a count of all event episodes. One participant may experience more than one event, and a registry may report whether participants had at least one event rather than the total number of events. The entries are labeled as participants affected or at risk. The registry record does not provide enough detail to determine whether event categories overlap or how repeated events were handled.

The number at risk supplies context for the affected-participant count. For the acute and late safety groups, 50 participants are listed at risk. However, the entries do not tell the reader whether every participant completed the same duration of follow-up, whether all assessments were available, or whether anyone was excluded from a particular analysis. Those details are not reported in the registry record.

Why does uncertainty matter?

General statistical explanation: a confidence interval is a range of values compatible with the observed data under a specified statistical model. It conveys uncertainty around an estimate; it is not a guarantee that the true value lies in the interval. In safety studies, uncertainty is important even when no serious events are recorded, because a finite study cannot rule out uncommon events. The registry record does not report a confidence interval for the primary endpoint or for the safety counts, so the precision of an endpoint estimate cannot be evaluated from the posted entries alone.

General statistical explanation: an event rate or proportion is most informative when its definition, denominator, follow-up duration and missing-data handling are clear. A proportion based on participants followed for different lengths of time may not have the same interpretation as one based on a common follow-up schedule. The registry specifies an acute and a late period and states that the primary endpoint is assessed up to 5 years, but it does not report person-time methods, follow-up completeness, or a detailed account of censoring.

What can a single-group design establish?

In a single-group study, observed outcomes can be described for participants who received the intervention. Without a comparison group, the analysis cannot directly estimate how those outcomes differ from outcomes under another treatment. Differences that might be observed in a controlled study could reflect the intervention, participant characteristics, other care, natural variation, or other factors. A single-group design does not remove these alternative explanations.

The registry lists no masking and no allocation to different groups. These design features are part of the context for interpreting outcomes, not proof that measurement or conduct was biased. For subjective outcomes such as quality of life, pain and cosmetic assessments, blinding can affect assessment in some study settings; whether and how this was addressed is not reported in the registry record. No outcome results for those measures are reported in the registry record.

How should statistical plans be interpreted?

A statistical analysis plan would normally describe how outcomes are defined and analyzed, which participants enter each analysis, how missing data are treated, and whether adjustments or subgroup analyses are planned. The registry record does not report those details. It also does not report an interim-analysis plan or a sample-size justification. Consequently, no claim should be made about a prespecified testing strategy, adjustment method, or intended precision.

General statistical explanation: when studies test several outcomes, multiplicity refers to the increased chance of obtaining at least one apparently notable result by chance when many hypotheses are assessed. Approaches such as prespecifying a primary outcome or adjusting for multiple tests can address this issue, but the registry record does not document an adjustment strategy. The existence of several listed secondary outcomes does not show that each was formally tested or that any result was statistically significant.

Sample-size calculations are planning tools based on assumptions; they are not observed power and do not reveal the certainty of results after data collection. The registry record does not report the trial’s own sample-size rationale. Any planning illustration should be distinguished from the completed study’s observed counts, and should not be treated as evidence that the study had adequate power for its outcomes.

In general, statistical significance and clinical importance are different ideas. A small p-value, if reported, would address compatibility with a statistical null model under assumptions; it would not by itself establish importance, causality, or safety. No p-value or analysis estimate for the primary endpoint is reported in the registry record. The available interpretation should therefore remain anchored in the recorded counts and in the design’s limits.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary safety outcome and secondary outcomes addressing regional lymph nodes, distant metastases, quality of life, pain and cosmetic measures. The results for these secondary outcomes are not reported in the registry record. The statistical plan for handling multiple outcomes or tests is also not reported in the registry record. General statistical explanation: assessing many outcomes can increase the chance of a result that appears notable by chance, so interpretation depends on knowing which analyses were prespecified and whether any multiplicity strategy was used. Those details cannot be established from the registry entry.

Missing-data handling and analysis populations are not reported in the registry record. The enrollment figure is 50, and the safety groups each list 50 at risk, but those details alone do not establish whether every participant completed all follow-up assessments or contributed to every outcome analysis. The record does not state how incomplete visits, withdrawals, missing measurements or losses to follow-up were handled. Nor does it report whether the analyses used all enrolled participants, only participants who received treatment, or another defined population.

These omissions matter because incomplete follow-up can affect the interpretation of safety and longer-term outcomes. If participants with missing assessments differ from those observed, the recorded outcomes may not represent the experience of all enrolled participants. Without information on follow-up completion and analysis rules, the direction or size of any such effect cannot be determined. The safety counts should be interpreted as recorded counts, with these reporting limitations in mind.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists an acute and a late treatment group, each with 50 participants at risk. For serious events, the affected-participant count is 0 in each group. The registry also lists 32 participants with other events in the acute group and 48 in the late group. Deaths are recorded as 0 in the acute group and 4 in the late group.

These entries are counts, not a full description of individual event types, timing or severity. The record does not provide the specific events represented by the “other” category, whether participants appear in more than one category, or whether all events were judged treatment-related. The death count is reported separately, and the registry record does not attribute those deaths to therapy. The serious-event counts are relevant to the primary safety question, but no confidence interval or separate primary-endpoint analysis is reported. The counts should not be interpreted as proof that serious toxicity cannot occur or as evidence of comparative safety.

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

The registry record describes a single-group study of single-fraction high-gradient partial-breast irradiation after partial mastectomy. Its primary safety question concerns serious treatment-related toxicity during follow-up up to 5 years. The recorded serious-event counts are zero in both the acute and late groups, each of which lists 50 participants at risk. Those counts are a useful description of the posted safety data, but their interpretation is limited by the absence of a reported confidence interval, analysis details and follow-up completeness information.

The record also lists other events and deaths. Those entries should be kept distinct from the primary endpoint: the registry does not report that the deaths were caused by treatment, and the types and attribution of other events are not detailed in the safety fields. Zero recorded serious events does not prove that the true risk is zero, particularly when the registry record does not explain the precision of the estimate or the extent of complete follow-up.

The study does not include a control group. It therefore cannot establish how the observed counts compare with outcomes under another radiation schedule, whole-breast treatment or another approach. Any apparent favorable or unfavorable outcome cannot be assigned to the intervention through a direct comparison in this design.

The study’s stated interests also include cancer outcomes, quality of life, pain and cosmesis. Results for those outcomes are not reported in the registry record. The absence of those results does not show that the outcomes were unchanged; it means that conclusions about them cannot be drawn from the reported record. Overall, the posted information supports a limited description of safety counts in the treated group, not a conclusion about comparative effectiveness or the full balance of benefits and harms.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of the distinction between describing outcomes and estimating a treatment effect. A single-group study can document what was recorded among participants who received an intervention. It cannot, without a comparator, show whether the observed outcomes would have been different under another treatment. That distinction is particularly important when the study’s aims include both safety and how well treatment works.

The safety endpoint also illustrates why outcome definitions and follow-up windows matter. Acute and late toxicity are treated as separate periods in the registry record, and the primary outcome focuses on serious treatment-related toxicity. A reader needs to distinguish that endpoint from the broader counts of other events and from deaths. Keeping these categories separate prevents a broad safety count from being mistaken for the specific endpoint or for a causal attribution.

The study’s listed outcomes span several domains: toxicity, cancer status, quality of life, pain and appearance. A broad set of outcomes can be useful for understanding what investigators intended to assess, but it also makes transparent reporting of outcome definitions, analysis methods and missing data important. The registry record does not report results for the listed secondary outcomes or details of a multiplicity strategy.

Finally, a zero count is not the same as proof of no risk. Statistical interpretation requires attention to uncertainty, follow-up and the number of observed participants, as well as to the design’s ability to support causal claims. The record gives useful descriptive context, but the limitations of the available reporting should guide how narrowly those observations are interpreted.

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 study has no control group, and the registry lists a single-group model with allocation recorded as NA. Consequently, the posted outcomes cannot provide a direct comparison with another treatment or establish a causal treatment effect. The absence of masking is recorded as NONE; the registry does not describe whether outcome assessment procedures addressed the possibility that knowledge of treatment could influence subjective assessments.

The enrollment is 50, but the registry record does not report a sample-size justification or the intended precision for the primary safety endpoint. It also does not report a confidence interval or a distinct analysis estimate for that endpoint. With no reported uncertainty measure, the precision of the observed serious-event counts cannot be assessed from the record alone.

Details needed to interpret the safety counts are limited. The record does not specify the types of events included in the other-event counts, provide participant-level timing, or state whether event categories overlap. The four deaths in the late group are not assigned a cause or attributed to treatment in the posted safety fields. Follow-up completeness, missing assessments, withdrawals and analysis populations are not reported in the registry record.

The registry lists outcomes for regional lymph nodes, distant metastases, quality of life, pain and cosmesis, but their results are not reported in the registry record. The statistical plan, including handling of multiple outcomes, is also not reported. Further details about eligibility, radiation dose and delivery, concurrent or subsequent care, and the rationale for treatment selection are not reported in the registry record. These gaps restrict interpretation of both the safety findings and the broader clinical questions described by the study.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Single Fraction High-Gradient Partial Breast Irradiation in Treating Patients With Low-Risk Stage 0-I Breast Cancer — NCT02076074.
• Registry record last updated 2024-07-11; status last verified 2024-06.
• Results first posted 2024-07-11.
• 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

NCT02076074 is a completed single-group study sponsored by Washington University School of Medicine. The registry lists an enrollment of 50, allocation as NA, masking as NONE and a SINGLE GROUP model. The phase field is NA; the brief summary calls the study phase I/II. The study began on 2014-04-02, and primary completion was recorded as 2023-05-18.

The intervention was accelerated partial-breast irradiation, described as single-fraction high-gradient partial-breast irradiation within 8 weeks after partial mastectomy. The primary outcome concerns freedom from serious treatment-related toxicity up to 5 years. The serious-event fields record zero affected participants in the acute and late groups, each listing 50 at risk. Other events and deaths are also recorded, but the registry provides limited detail about their nature and attribution. Results for the listed secondary outcomes and a detailed analysis plan are not reported in the registry record.