Study of Safety and Efficacy of a Sequential Regimen Consisting of Three Cycles of Fludarabine Followed by Tositumomab and Iodine I 131 Tositumomab: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of Safety and Efficacy of a Sequential Regimen Consisting of Three Cycles of Fludarabine Followed by Tositumomab and Iodine I 131 Tositumomab (NCT00933335), a na phase 2 study. The primary outcome is Number of Participants With Any Adverse Event (AE).

2. Clinical Question

This is a descriptive safety question rather than a treatment-versus-control question. The registry record does not specify an untreated or alternative-treatment comparator, and its allocation entry is NA. As a result, the posted event counts can describe what was recorded during treatment, but they cannot by themselves establish how event occurrence compares with another treatment or with what would have occurred without the regimen.

The record lists secondary outcomes covering confirmed and unconfirmed responses, progression, response duration, time to progression or death, treatment failure, and time to treatment failure. The outcome names indicate what investigators planned to assess, but outcome values are not reported in the registry record. The clinical question about efficacy therefore cannot be answered from the posted results.

3. Trial Design

The registry record describes a completed phase II, single-arm, single-institution study. It lists 38 participants enrolled, allocation as NA, and masking as none. The study start is recorded as 1998-08 and primary completion as 2009-12. The stated purpose was to evaluate the safety of fludarabine followed by Iodine I 131 tositumomab, with efficacy as a secondary endpoint.

The regimen was sequential. Participants were to receive three cycles of fludarabine, described as 25 mg/m2 for 5 days every 5 weeks. Iodine I 131 tositumomab was to begin 6 to 8 weeks after completion of fludarabine. The arm description also refers to dosimetry to determine patient-specific activity, but the rest of that description is not reported in the registry record. The intervention is listed as tositumomab and Iodine I 131 tositumomab.

A single-group design means the study does not provide a randomized, concurrent control group for estimating a between-group treatment effect. The three safety groupings in the posted results correspond to fludarabine, TST and Iodine I 131 TST, and the combined regimen. They are not like-for-like control arms. Participants could be represented in more than one treatment-period grouping; the record does not describe these as independent samples.

The primary adverse-event population is defined as the intent-to-treat exposed population: enrolled participants who received at least one fludarabine dose. The data are presented for the subgroup who received both the dosimetric and therapeutic TST/I 131 TST doses. The adverse-event entries list different numbers at risk for treatment groupings, so denominators should be read alongside each reported count rather than assumed to be identical across periods.

The registry record does not report a detailed statistical analysis plan, a sample-size justification, or interim-analysis procedures. The enrollment figure describes the study record, not a control-group allocation or an efficacy comparison.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Participants received fludarabine in the first study phase. Upon completion of this phase, if they met the appropriate criteria, they began the first of 2 phases of radioimmunotherapy: Phase 1, dosimetric dose (DD), administered 6 weeks after Day 1 of the third fludarabine cycle; Phase 2, therapeutic dose, administered 7-14 days after the DD.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intent-to-Treat (ITT)-Exposed Population: all participants who were enrolled into the study and who received at least 1 dose of fludarabine. The data are presented for the subgroup of the ITT-Exposed Population for those participants who received the dosimetric and therapeutic dose of TST/I 131 TST.

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 Number of Participants With Any Adverse Event (AE), measured over First day of fludarabine cycle 1 to day prior to TST and iodine I 131 TST dosimetric dose (DD) (Week -16 to Week 1); Day of TST and iodine I 131 TST DD to database release (Week 1 to Week 520).

The primary endpoint is the number of participants with any adverse event. An adverse event was defined as an untoward medical occurrence after administration of a pharmaceutical product; a causal relationship to treatment was not required. Laboratory abnormalities counted as adverse events only when they were associated with clinical sequelae and/or required an intervention.

This endpoint is used to describe safety during treatment and follow-up. Counting participants who experienced at least one event gives a straightforward summary of how many people had an event in the defined population and period. It does not describe the total number of events per participant, the severity distribution of all events, or whether an event was caused by treatment. Those questions require additional outcome definitions and results.

The registry record divides the observation window into the period from the first day of fludarabine cycle 1 to the day before the TST and Iodine I 131 TST dosimetric dose (Week -16 to Week 1), and the period from the day of that dosimetric dose to database release (Week 1 to Week 520). These intervals span different treatment phases and follow-up durations, so counts for them should be interpreted with their stated timeframes in mind. The primary outcome is a count of participants with an event, not a comparison of event rates between randomized groups.

The registry record also provides serious adverse-event counts by regimen grouping. Serious events are distinct from the broader any-adverse-event endpoint; the record's definition of any adverse event does not imply that every event was serious or treatment-related.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record reports a primary outcome expressed as the number of participants with any adverse event. This is a count of people meeting an event criterion, rather than a count of every occurrence. A participant with several events may still contribute only once to a measure defined as the number of participants with any event. The record does not provide a total event count for this primary endpoint.

What does a participant count tell us?

A participant count is easy to interpret descriptively: it indicates how many people in a defined group experienced at least one event during a stated period. It is most informative when read with the number at risk and the time window. Counts alone do not adjust for differences in group size or follow-up time. A proportion or rate could support other comparisons, but new values should not be inferred from the posted counts when those calculations are not reported.

The primary outcome definition matters. The registry record counts an untoward medical occurrence as an adverse event without requiring a causal link to treatment. It also states that laboratory abnormalities were recorded only if associated with clinical sequelae and/or requiring an intervention. This definition describes the scope of event capture; it does not say that every listed event was caused by the study regimen. Attribution and severity are separate considerations.

Why are there several treatment groupings?

The safety results are listed for fludarabine, TST and Iodine I 131 TST, and the combined regimen. In a sequential regimen, these labels describe treatment periods or exposures. They should not be treated as randomized arms. A valid randomized comparison ordinarily relies on groups assigned to different strategies under a common design; this study is listed as single-group, with allocation NA. The posted group counts therefore support descriptive reading, not a causal comparison between treatments.

The numbers at risk are 38 for the fludarabine grouping, 35 for the TST and Iodine I 131 TST grouping, and 38 for the combined regimen grouping. The record identifies the primary safety population as enrolled participants who received at least one fludarabine dose, and says the data are presented for the subgroup receiving dosimetric and therapeutic TST/I 131 TST doses. It does not give a participant flow account explaining the group-specific denominators. The denominators should therefore be retained as reported and not combined.

How should uncertainty be understood?

Any count from a study population is subject to uncertainty about how well it represents outcomes that might be seen in similar patients and settings. A confidence interval is a statistical range constructed to express uncertainty around an estimate under specified assumptions. It is not a guarantee that the true value lies within that range, and it does not address biases caused by study design or incomplete reporting. Confidence intervals for the posted adverse-event results are not reported in the registry record.

For event data, variation in underlying event frequency can be more pronounced than a simple model assumes. General statistical methods may account for over-dispersion when observed variability exceeds the model’s expected variability. Whether an over-dispersion adjustment was used in this study is not reported in the registry record. The record also does not report the specific statistical model used for the primary safety endpoint.

What do the planning assumptions mean?

General sample-size planning asks how much information a future study would need to detect a prespecified effect under stated assumptions. The planning assumptions associated with this record describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect set as a stated fraction of the observed effect. These assumptions describe planning illustrations, not the design of the single-group study itself. Such calculations are not observed power, and they do not demonstrate that the original study was adequately powered.

For time-to-event outcomes, general planning methods often use the number of events as the key information quantity; other outcome types may use participants per arm. The registry record lists time-to-event secondary outcomes, but it does not report their results or the statistical analysis used for them. A study’s actual sample-size justification and the details of its analysis plan are not reported in the registry record.

The record lists 35 outcome measures and zero analyses. This indicates that outcome measures are listed without corresponding analyses in the registry record; it does not establish that no analyses were performed outside the record. No recalculated comparison or adjusted effect estimate is reported in the registry record.

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.

R code and output

arm    <- c("Fludarabine", "TST and Iodine I 131 TST", "Fludarabine/TST and Iodine I 131 TST (Combined Reg")
n      <- c(38, 35, 38)
events <- c(33, 34, 38)
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  Fludarabine  38  33  86.8  71.9  95.6  72.7  94.2  72.6  94.1
ARM  TST and Iodine I 131 TST  35  34  97.1  85.1  99.9  85.5  99.5  85.5  99.3
ARM  Fludarabine/TST and Iodine I 131 TST (Combined Reg  38  38  100.0  90.7  100.0  90.8  100.0  91.0  99.9

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists several secondary outcomes: confirmed and unconfirmed investigator-assessed responses, progression of disease, duration of response, time to disease progression or death, treatment failure, and time to treatment failure. Testing or estimating multiple outcomes raises a general multiplicity issue: as the number of statistical questions increases, the chance of at least one apparently notable result can increase if each is treated as a separate confirmatory test. Whether this study used a prespecified hierarchy, adjustment, or other multiplicity strategy is not reported in the registry record.

Outcome names are not outcome findings. Values for the listed secondary efficacy measures are not reported in the registry record, and the record does not specify which secondary outcomes were analyzed or how missing outcomes were handled. No imputation method, censoring convention, or sensitivity analysis for missing data is reported in the registry record.

The primary population is described as enrolled participants who received at least one dose of fludarabine, with safety data presented for those who received dosimetric and therapeutic TST/I 131 TST doses. This definition helps identify who contributes to the reported safety data, but the record does not provide a full accounting of exclusions, treatment completion, or follow-up availability for every outcome. It also does not report whether the efficacy outcomes used the same population.

The registry record does not report a detailed statistical analysis plan, including prespecified handling of missing observations or multiplicity. Consequently, the posted results do not support an assessment of whether analysis choices were prespecified or how robust the findings are to alternative assumptions.

12. Safety Results

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

Other (non-serious) adverse events

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

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: febrile neutropenia (7.9%), myelodysplastic syndrome (5.7%), acute myeloid leukaemia (2.9%), chronic myelomonocytic leukaemia (2.9%), prostate cancer (2.9%).

The serious adverse-event counts are 2 of 38 for fludarabine, 7 of 35 for TST and Iodine I 131 TST, and 8 of 38 for the combined regimen. The associated any-adverse-event counts are 33 of 38, 34 of 35, and 38 of 38, respectively. These are participant counts within the listed regimen groupings. The sequential, single-group design means the groupings are not a like-for-like control comparison.

The registry record also lists the following serious-event terms and percentages: febrile neutropenia, 7.9%; myelodysplastic syndrome, 5.7%; acute myeloid leukaemia, 2.9%; chronic myelomonocytic leukaemia, 2.9%; prostate cancer, 2.9%; and squamous cell carcinoma, 2.9%. The record does not report the denominator or further details for these term-level percentages. They should not be converted into counts or assumed to represent mutually exclusive participants.

Deaths are not reported in the registry record. A missing value is not evidence that no deaths occurred. Similarly, the broad adverse-event definition does not establish that an event was caused by treatment; the record states that causality was not required for an event to qualify.

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

The registry record supports a descriptive account of adverse events recorded during a sequential fludarabine and TST/I 131 TST regimen in a phase II, single-group study. It reports participants with serious and any adverse events in treatment groupings, and it lists several serious-event terms with percentages. These results describe what was recorded for the reported populations and timeframes.

They do not establish a causal treatment effect. There was no randomized comparator, and the regimen groupings are not independent control arms. Differences between their counts cannot isolate the effect of one treatment component from the influence of treatment sequence, eligibility for later treatment, or differences in observation. The registry record does not provide an analysis that adjusts for these factors.

The counts also do not establish the frequency of all event episodes, the timing of each event, or the probability of an event in a broader population. The registry record does not report confidence intervals for these results, and the term-level percentage denominators are not reported. The definition of an adverse event does not require causal attribution, so the counts should not be described as events caused by treatment.

Efficacy is not interpretable from the posted results. Although response and progression outcomes are listed, their values are not reported in the registry record. The listed outcomes do not show that the regimen did or did not produce responses, delay progression, or affect treatment failure. No conclusion about comparative efficacy can be drawn from the information reported.

Overall, the record offers safety counts for the specified groupings and descriptions of the outcomes the study intended to assess. It does not provide the comparative design, precision estimates, or efficacy results needed to make broader claims about treatment effects.

14. Why This Trial Matters Statistically

This study illustrates why design determines the questions an analysis can answer. A single-group trial can describe adverse events observed during a treatment sequence, but it cannot provide the same direct treatment contrast as a randomized study with a concurrent control. Reading the treatment-period groupings as if they were randomized arms would give the counts a meaning that the design does not support.

It also highlights the importance of defining the safety population and timeframe. The primary endpoint uses an intent-to-treat exposed population definition and presents data for the subgroup receiving dosimetric and therapeutic TST/I 131 TST doses. The reported numbers at risk differ across treatment groupings. Clear population definitions help readers understand which participants contribute to a result; incomplete participant-flow details make it harder to explain why denominators differ.

The distinction between an adverse event and a treatment-related event is another central statistical and clinical issue. The registry definition does not require a causal relationship. Counts can therefore characterize safety observations without establishing attribution. Serious-event terms and any-event counts also answer different questions and should not be conflated.

Finally, a registry record can list a wide range of planned outcomes without reporting their values or the analysis procedures. Here, efficacy outcomes are named, but their results and the statistical analysis plan are not reported in the registry record. This makes transparent outcome reporting essential: readers need estimates, uncertainty measures, population definitions, and analysis details to evaluate what the findings mean. The record is therefore useful both for the adverse-event counts it documents and for identifying limits on the conclusions that can be drawn.

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 principal limitation is the single-group design. With no randomized control arm, the posted results cannot estimate a causal difference between the regimen and another treatment. The treatment-period groupings do not supply a substitute for a concurrent comparator, and their counts should not be interpreted as independent-arm comparisons.

The registry record does not report confidence intervals for adverse-event counts, details of the statistical methods used, or the analysis plan. It also does not report a sample-size justification or interim-analysis procedures. The seriousness-term percentages are listed without their denominators or further calculation details. These omissions limit assessment of precision and analytical choices.

The primary population definition is available, but participant flow and the reasons for differing numbers at risk across groupings are not reported in the registry record. The record also does not provide complete details about follow-up for each outcome. The primary endpoint spans specified periods from fludarabine cycle 1 through database release, but results for the listed efficacy outcomes are not reported.

The adverse-event definition does not require a causal relationship, so the event counts cannot establish treatment attribution. Deaths are not reported in the registry record; that absence should not be interpreted as a finding of zero deaths. Finally, the record’s list of secondary outcomes does not establish that each was analyzed, and its detailed approach to multiplicity and missing data is not reported.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study of Safety and Efficacy of a Sequential Regimen Consisting of Three Cycles of Fludarabine Followed by Tositumomab and Iodine I 131 Tositumomab — NCT00933335.
• Registry record last updated 2017-01-18; status last verified 2016-11.
• Results first posted 2012-03-13.
• 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.

19. Record Summary

NCT00933335 is a completed phase II, single-arm, single-institution study of fludarabine followed by tositumomab and Iodine I 131 tositumomab in previously untreated, advanced-stage low-grade, transformed low-grade, or follicular non-Hodgkin's lymphoma. The record lists 38 participants enrolled, with a study start of 1998-08 and primary completion of 2009-12. Masking is listed as none and allocation as NA.

The primary endpoint was the number of participants with any adverse event. The posted safety results include serious and any-adverse-event counts for fludarabine, TST and Iodine I 131 TST, and the combined regimen. These are descriptive groupings, not randomized comparison arms. The registry record lists secondary response and disease-control outcomes but does not report their values. A detailed statistical analysis plan, confidence intervals, missing-data methods, and deaths are not reported in the registry record.