Pivotal Study of Iodine I 131 Tositumomab for Chemotherapy-refractory Low-grade or Transformed Low-grade B-cell Non-Hodgkin's Lymphoma: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pivotal Study of Iodine I 131 Tositumomab for Chemotherapy-refractory Low-grade or Transformed Low-grade B-cell Non-Hodgkin's Lymphoma (NCT00989664), a na phase 2 study. The primary outcome is Number of Participants (Par.) Receiving TST and I 131 TST With a Response >=30 Days Versus Par. With a Response >=30 Days After Their Last Qualifying Chemotherapy Regimen (LQCR), Masked Independent Randomized Radiology and Oncology Review (MIRROR) Panel.

2. Clinical Question

3. Trial Design

The registry describes a completed, open-label, single-group study of tositumomab and iodine I 131 tositumomab in chemotherapy-refractory low-grade B-cell lymphomas and low-grade lymphomas transformed to higher-grade histologies. Enrollment was 60. The registry classifies the phase as Phase 2, while the official title calls the study a pivotal Phase III study. Both descriptions appear in the registry record; it does not explain the difference in phase wording.

Allocation is listed as not applicable, and the model is listed as single-group. The intervention is described as an open-label single arm. This means the primary comparison is not a randomized comparison between participants assigned to study treatment and participants assigned to chemotherapy. Instead, the outcome description uses participants’ response after the study treatment and their response after their own last qualifying chemotherapy regimen. The prior regimen is therefore a historical, within-participant comparator.

The primary outcome was assessed by a masked independent radiology and oncology review panel, even though the treatment arm is described as open-label. The outcome definition also lists investigator-assessed secondary outcomes, including response categories, time to progression or death, time to treatment failure, overall survival, responses after study treatment and LQCR, and adverse events. The registry record lists 22 outcome measures and one analysis, but does not describe the analysis methods or provide results for those outcomes in the registry record recorded.

The study started in 1996-11 and had primary completion in 2004-01. The study status is completed. Participants were evaluated for up to 99.1 months in Study 104504 or followed in a long-term follow-up study for up to 141.5 months, according to the primary outcome timeframe. These are stated maximum follow-up periods, not descriptions of the follow-up received by every participant. The registry record does not give individual follow-up distributions or explain how follow-up was handled analytically.

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 (par.) received radioimmunotherapy of tositumomab (TST) and Iodine I 131 TST in 2 phases (Ph.): Ph. 1, dosimetric dose; Ph. 2, therapeutic dose. Par. were evaluated until disease progression, they died, or they were on study for 2 years. Par. completing 2 years of study could enter a long-term follow-up study (BEX104526; NCT00240591).

Dosimetric and Therapeutic Treatment

Reasons for not completing this period:

Long-Term Follow-Up

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: ITT Exposed Population

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 (Par.) Receiving TST and I 131 TST With a Response >=30 Days Versus Par. With a Response >=30 Days After Their Last Qualifying Chemotherapy Regimen (LQCR), Masked Independent Randomized Radiology and Oncology Review (MIRROR) Panel, measured over Participants were evaluated for up to 99.1 months in Study 104504 or were followed in the long-term follow-up study for up to 141.5 months.

The primary outcome counts participants whose response lasted at least 30 days after tositumomab and iodine I 131 tositumomab and compares that count with participants whose response lasted at least 30 days after their last qualifying chemotherapy regimen. The response categories are complete response, complete response unconfirmed, and partial response. Complete response requires resolution of disease-related radiological abnormalities and disappearance of disease-related signs and symptoms. Complete response unconfirmed meets the characteristics of complete response except that nodal size has not regressed sufficiently or bone marrow findings are indeterminate. Partial response is defined as at least a 50% reduction in the sum of the products of the longest perpendicular diameters of measurable lesions, with no new lesions.

The 30-day duration criterion makes the endpoint more specific than simply recording any response at a single assessment. A count is also straightforward to interpret: it indicates how many participants met the stated response definition. The masked independent review panel is specified for this primary comparison, which distinguishes it from the secondary outcomes described as investigator assessed.

Because the comparator is each participant’s previous LQCR, the endpoint can describe response status across sequential treatments within the study population. It cannot, by itself, provide the same protection against differences in treatment groups that random allocation to a concurrent control would provide. The registry record does not report the response counts, the size or direction of the comparison, an uncertainty interval, or a significance test. The endpoint definition is available, but the numerical primary result is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is a binary participant-level outcome: a participant either met the specified response definition lasting at least 30 days or did not. The response categories include complete response, complete response unconfirmed, and partial response. A count of participants meeting the endpoint is a natural way to report such an outcome. A count alone, however, does not describe how uncertain an estimated response frequency or comparison may be; that also depends on the analysis and the amount of outcome information available.

What does a confidence interval convey?

In general, a confidence interval expresses statistical uncertainty around an estimate. Its width reflects how precisely the data estimate the quantity of interest under the analysis assumptions. A narrow interval indicates greater precision than a wide interval, while an interval that includes values representing little or no difference may leave the direction or size of a comparison uncertain. The registry record does not report a confidence interval for the primary outcome, so the precision of the primary comparison cannot be assessed in the registry record recorded.

What is distinctive about this comparator?

The primary comparison uses the participant’s own last qualifying chemotherapy regimen as the comparator. This is a historical, within-participant comparison: the study treatment follows the prior chemotherapy. It differs from a concurrent randomized design, in which participants are assigned to different treatment groups during the same study period. A prior-treatment comparison can be affected by changes over time, differences in the circumstances of treatment, and how participants are selected for later treatment. These are general design considerations, not claims about what occurred in this study. The registry record does not report an adjustment strategy or details sufficient to assess these issues.

The masked independent radiology and oncology review panel is named for the primary outcome. In general, masking outcome assessors can reduce the chance that knowledge of treatment influences outcome classification. The study itself is described as open-label, and the record does not explain the panel’s procedures, how masking was maintained, or how disagreements were resolved. The panel designation should therefore be read as part of the stated outcome method, not as proof that all potential assessment bias was eliminated.

What do the response definitions contribute?

The endpoint combines complete response, complete response unconfirmed, and partial response, provided the response lasted at least 30 days. The category definitions specify radiological and clinical features for complete response and a lesion-reduction criterion for partial response. These definitions make the endpoint more operational than an unspecified judgment of improvement. Combining categories can make the primary endpoint easier to summarize, but it also means that a single total does not reveal how many participants fell into each response category. The registry record lists further response outcomes, but does not report their results in the registry record recorded.

What can the sample-size assumptions tell us?

The sample-size assumptions describe a planning illustration based on the observed effect, rather than the trial’s own design justification. The stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect expressed as a fraction of the observed effect. For time-to-event outcomes, the illustration uses a total number of events under the Schoenfeld approach; for other outcomes, it expresses participants per arm. These are planning conventions, not observed trial findings and not observed power. The registry record does not report the trial’s sample-size justification, and the planning assumptions alone do not establish how the study was designed or whether it had adequate precision.

The study is recorded as a single-group study, while the planning assumptions refer to equal allocation between two arms. That planning illustration should not be mistaken for the actual study allocation. The registry record gives allocation as not applicable and the model as single-group. Specific planning counts are not reported in the registry record.

What analysis details are absent?

The record identifies the primary outcome population as the ITT Exposed Population and describes one analysis. It does not report the primary response counts, the statistical test, an effect measure, a confidence interval, or a p-value. It also does not describe a covariate-adjustment method, handling of missing outcomes, or a sensitivity analysis. Without those details and the outcome results, an independent assessment of the statistical evidence is not possible. The registry record does not report an interim-analysis plan or a detailed statistical analysis plan.

General statistical interpretation should separate the endpoint definition, the observed estimate, and uncertainty around that estimate. The definition and design are described, but the primary numerical estimate and its uncertainty are not reported in the registry record. Consequently, no claim about the size, direction, or precision of the primary comparison can be supported in the registry record recorded.

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("TST and I 131 TST", "LQCR")
n      <- c(60, 60)
events <- c(26, 5)
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  TST and I 131 TST  60  26  43.3  30.6  56.8  31.6  55.9  31.5  55.9
ARM  LQCR  60  5  8.3  2.8  18.4  3.6  18.1  3.7  18.1

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 22 outcome measures and one analysis. It names multiple secondary outcomes, including unconfirmed and confirmed response categories, time to progression or death, time to treatment failure, overall survival, response after study treatment and after LQCR, and adverse events. A study that considers multiple outcomes or response categories raises a general multiplicity question: the more statistical comparisons considered, the greater the chance that at least one result may appear notable by chance if no adjustment or prespecified hierarchy is used.

The record does not report a multiplicity adjustment, a testing hierarchy, or which secondary outcomes were included in formal hypothesis tests. It also does not report whether the primary outcome was analyzed as a formal confirmatory test or how the different listed measures were handled. These details are not reported in the registry record, so no conclusion about control of multiplicity can be made.

The primary outcome population is identified as the ITT Exposed Population. The registry record does not give the number analyzed for that outcome or explain the relationship between enrollment and the analysis population. It does not describe how missing response assessments, withdrawals, or incomplete follow-up were handled. Those matters can affect a participant-count endpoint and time-to-event outcomes, but the specific handling in this study is not reported in the registry record.

The primary timeframe allows evaluation for up to 99.1 months in Study 104504 or follow-up in a long-term study for up to 141.5 months. These maximum periods do not reveal the completeness of follow-up or the amount of missing outcome information. No interim-analysis plan, missing-data method, or sensitivity analysis is reported in the registry record.

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: myelodysplastic syndrome (6.7%), squamous cell carcinoma (5.0%), pleural effusion (5.0%), basal cell carcinoma (3.3%), non-hodgkin's lymphoma (3.3%).

For the TST and I 131 TST group, the record reports serious adverse events in 30 participants among 60 at risk, and other adverse events in 59 participants among 60 at risk. These are participant counts within the treatment group. They describe how many participants experienced at least one event in each reported category; they do not give the total number of event episodes or the timing of events.

The listed serious adverse event terms include myelodysplastic syndrome at 6.7%, squamous cell carcinoma at 5.0%, pleural effusion at 5.0%, basal cell carcinoma at 3.3%, Non-Hodgkin’s lymphoma at 3.3%, and squamous cell carcinoma of skin at 3.3%. These are the selected terms and percentages reported in the registry record, not a complete narrative of each participant’s safety experience.

Because the study is single-group, these figures do not provide a randomized comparison of adverse event frequency. The record does not report a concurrent control group or an attribution breakdown for the overall counts in the registry record recorded. An event occurring during a study is not, on its own, proof that the study treatment caused it. The listed figures should be read as descriptive safety reporting within the treated group, with the registry record’s limitations in mind.

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

The record gives a defined primary response question for tositumomab and iodine I 131 tositumomab in chemotherapy-refractory low-grade or transformed low-grade B-cell non-Hodgkin’s lymphoma. It specifies response categories, a duration threshold of at least 30 days, a masked independent review panel, and a comparison with each participant’s last qualifying chemotherapy regimen. It also describes a single-group, open-label study and reports enrollment of 60 participants.

Those features do not establish the numerical result of the primary comparison. The registry record does not report how many participants met the response definition after study treatment or after LQCR, nor does it report an effect estimate, confidence interval, or p-value. Thus, the magnitude, direction, and precision of the comparison cannot be determined from the record. The design and endpoint definition should not be mistaken for evidence about the outcome.

The historical within-participant comparator has a different interpretation from a concurrent randomized control. A comparison across sequential treatments may be informative as a description of participants’ responses, but it does not isolate treatment effects in the same way as randomized assignment. The registry record does not provide the outcome data or analysis details needed to assess the observed comparison.

The safety counts and selected serious adverse event terms describe events reported in the treatment group. Without a concurrent comparison and more detailed attribution and follow-up information, they do not establish how much of the observed event burden was caused by treatment or how it compares with another treatment.

Overall, the registry record supports a careful account of the study question, design, follow-up timeframe, and reported safety figures. It does not support a conclusion that the study treatment was better or worse than LQCR, nor a conclusion about the clinical importance of any response difference. Those judgments require primary outcome results and an analysis that are not reported in the registry record.

14. Why This Trial Matters Statistically

This study is statistically notable because its primary question sounds comparative, while its registered design is single-group. The comparison is between response after study treatment and response after each participant’s last qualifying chemotherapy regimen. Recognizing that distinction is important: a historical within-participant comparison and a randomized concurrent comparison answer related but not identical questions and carry different sources of uncertainty.

The outcome definition also illustrates how a clinical endpoint combines measurement rules with a time requirement. Responses include complete response, complete response unconfirmed, and partial response, and must last at least 30 days. The stated criteria make the response classification more explicit, while the combined endpoint still conceals the distribution across its component categories unless those categories are reported separately. The registry lists secondary response measures, but their results are not reported in the registry record.

The study also distinguishes the open-label treatment arm from the masked independent review used for the primary outcome. This is a useful reminder that masking can apply to outcome assessment even when the treatment group itself is open-label. It can address one part of outcome measurement, but it does not create random allocation or a concurrent comparator.

Finally, the record demonstrates why statistical interpretation depends on results as well as methods. Enrollment, endpoint definitions, and safety counts are meaningful descriptive information, but they cannot replace the primary response estimate and its uncertainty. Since those numerical results are not reported in the registry record, the central comparative question remains unquantified in the available record. This boundary between design information and outcome evidence is central to a cautious reading of clinical trial statistics.

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 primary response counts or a comparative estimate. It also does not give a confidence interval, p-value, or other measure of uncertainty. The stated endpoint can be described, but the magnitude and precision of its result cannot be assessed.

The comparator is the participant’s last qualifying chemotherapy regimen rather than a concurrently randomized control group. Allocation is listed as not applicable, and the study model is single-group. The registry record does not report an adjustment strategy for the sequential comparison or provide details for evaluating differences between the treatment periods. The masked independent review panel is specified for the primary outcome, but the masking procedures are not reported.

The record identifies the ITT Exposed Population but does not report the number analyzed for the primary outcome, the handling of missing assessments, or the flow of participants through follow-up. It gives maximum follow-up periods of up to 99.1 months in Study 104504 or up to 141.5 months in the long-term follow-up study; it does not describe how much follow-up each participant contributed.

Although the record lists 22 outcome measures and one analysis, it does not report a statistical analysis plan, multiplicity handling, interim analyses, or sensitivity analyses. Sample-size assumptions are described as a planning illustration based on the observed effect, not as the trial’s own design justification. The record does not provide the trial’s sample-size justification or specific planning counts in the registry record recorded.

The registry classifies the study as Phase 2, while its official title describes it as Phase III; the record does not explain the difference. Safety is reported descriptively for a single treatment group, without a concurrent control comparison in the registry record recorded. Together, these omissions limit assessment of comparative efficacy, statistical precision, missing-data effects, and comparative safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Pivotal Study of Iodine I 131 Tositumomab for Chemotherapy-refractory Low-grade or Transformed Low-grade B-cell Non-Hodgkin's Lymphoma — NCT00989664.
• Registry record last updated 2016-12-13; status last verified 2016-10.
• Results first posted 2012-04-10.
• 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

The registry record describes a completed, open-label, single-group study of tositumomab and iodine I 131 tositumomab for chemotherapy-refractory low-grade B-cell lymphoma or low-grade lymphoma transformed to higher-grade histology. Enrollment was 60 participants. The registry classifies the study as Phase 2; the official title describes it as Phase III.

The primary outcome counts responses lasting at least 30 days after study treatment and compares them with responses after participants’ last qualifying chemotherapy regimen. Response assessment is attributed to a masked independent radiology and oncology review panel. The record does not report the primary response counts or comparative result.

For the treatment group, serious adverse events were reported in 30 participants among 60 at risk, and other adverse events in 59 among 60 at risk. The listed serious event terms include myelodysplastic syndrome at 6.7%, squamous cell carcinoma at 5.0%, and pleural effusion at 5.0%. The study started in 1996-11 and had primary completion in 2004-01.