CELLO - CLiRpath® Excimer Laser System to Enlarge Lumen Openings: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for CELLO - CLiRpath® Excimer Laser System to Enlarge Lumen Openings (NCT00595959), a non-randomized phase 3 study. The primary outcome is Laser Success.

2. Clinical Question

This is a question about a procedural endpoint in the treated group, not a comparison of outcomes between assigned treatments. The registry identifies safety and efficacy as study objectives, but the primary endpoint concerns the immediate angiographic result. The listed endpoint population is per protocol; the registry record does not report a separate intention-to-treat primary analysis.

The description sets a threshold for success, but the numerical primary result is not reported in the registry record. Consequently, the record does not establish how many participants met the threshold or give the mean reduction and its variability. It also does not report a control-group result against which to assess the endpoint. These omissions limit what can be concluded from the posted results about the size and precision of the procedural outcome.

3. Trial Design

CELLO was a Phase 3, completed, nonrandomized, single-group study with no masking. The registry lists enrollment of 65 and one intervention, the CLiRpath Photoablation System. It identifies Spectranetics Corporation as the sponsor. The record gives a study start of 2006-11 and a primary completion of 2007-04.

The study objective was to evaluate safety and efficacy of the CLiRpath Photoablation Atherectomy System, comprising the Bias Sheath guiding catheter used with available CLiRpath Excimer Laser Catheters of 2.0 mm or smaller. The intended procedural purpose described in the record was to create larger lumens in the superficial femoral and popliteal arteries above the knee. The listed arm is Laser Treatment; no separate control arm is described.

Because there was no random allocation and no control group, the design does not support a direct randomized comparison of treatment strategies. The primary endpoint was assessed at the time of the procedure, after laser treatment and before adjunctive therapy. It used angiographic core laboratory assessment and a per-protocol population. The registry does not describe how the core laboratory assessment was conducted or how the per-protocol population was defined.

Enrollment and study status describe the trial record, not the number of participants with evaluable primary endpoint data. The registry does not report the number analyzed for laser success, the number excluded from that analysis, or reasons for any exclusions. A sample-size justification, interim-analysis plan, and detailed statistical analysis plan are not reported in the registry record.

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: Patients were screened for inclusion/exclusion criteria

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Per protocol

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 Laser Success, measured over Measured at time of procedure.

The primary endpoint, laser success, is defined as achieving an average reduction of at least 20% in percent diameter stenosis after laser treatment and before adjunctive therapy. The assessment was based on angiographic core laboratory review and was scheduled at the time of the procedure. The listed analysis population was per protocol.

This endpoint focuses on an immediate anatomical change at the treated site. A threshold-based definition can make a procedural outcome easier to classify: the result is judged against a prespecified level of stenosis reduction rather than against an unspecified impression of improvement. The record also describes the endpoint as a continuous measure, with the parameter reported as a mean and dispersion specified as a standard deviation. Those summaries would describe the average reduction and the spread of individual measurements, if numerical values were reported.

The registry record does not report the observed mean, standard deviation, or proportion meeting the success threshold. It therefore does not show the magnitude or precision of the measured change. Nor does it explain whether a separate binary success analysis was performed. The immediate angiographic endpoint should be distinguished from the listed secondary outcomes, which include procedural success, lumen diameters, clinical success, patency, stenosis measured by duplex ultrasound, Rutherford Classification, and adverse events. Those outcomes address different aspects of the study and do not substitute for the missing primary endpoint result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean describe?

In general, the mean is an average across the measurements included in an analysis. For a continuous endpoint such as percent reduction in stenosis, it can describe the central level of the measured reductions in the analyzed population. The mean does not show whether measurements were tightly grouped or widely dispersed, whether the distribution was strongly uneven, or whether a small number of observations had substantial influence. That is why the registry also specifies a standard deviation as the dispersion measure.

The registry names the endpoint parameter as a mean and the dispersion as a standard deviation, but it does not report their numerical values. No average reduction or amount of variability can therefore be read from this record. The mean also would not, by itself, say what fraction of participants met the threshold in the endpoint definition. A continuous summary and a threshold-based success classification answer related but different questions.

What does a standard deviation add?

In general, a standard deviation describes how spread out individual observations are around their mean. A smaller standard deviation indicates observations closer to the mean, while a larger one indicates more spread. It is not the same as a confidence interval: a standard deviation describes variability among observations, whereas a confidence interval describes uncertainty around an estimated quantity under a statistical model.

The registry specifies standard deviation but gives no value. It also does not report a confidence interval for the primary endpoint. Without the observed mean, standard deviation, analysis count, and any interval estimate, readers cannot judge either the distribution of individual endpoint values or the uncertainty around the estimated average.

How should a threshold endpoint be read?

The primary definition sets a success threshold at an average reduction of at least 20% in percent diameter stenosis. In general, a threshold turns a measured quantity into a classification: observations that meet the stated criterion count as successes under that definition, while those that do not meet it do not. This can be clinically and operationally interpretable, but the choice of threshold affects the classification. A value just on either side of the threshold may be similar as a measurement while being assigned a different category.

The record describes the primary endpoint as a mean continuous measure and defines success through a threshold. It does not give the number of participants meeting that threshold or specify a separate statistical analysis for a binary success rate. No rate or uncertainty for threshold-defined success should be inferred without those results.

What can a confidence interval tell a reader?

In general, a confidence interval gives a range of values compatible with an estimate under the assumptions of the analysis. Its width conveys precision: a narrower interval indicates less statistical uncertainty than a wider interval, all else being comparable. It is not a guarantee that the true value falls in the interval, and it does not address every source of bias. In a single-group study, an interval around an average could characterize uncertainty in that group’s estimate, but it would not create a control comparison or remove limitations of the design.

No confidence interval for laser success is reported in the registry record. No interval should be reconstructed from the enrollment count alone; the necessary endpoint summary statistics and analysis details are not present.

What is over-dispersion, and is it relevant?

In general, over-dispersion means that observed variability is greater than a statistical model expects. It is particularly relevant for count outcomes analyzed with models that assume a particular mean-to-variance relationship. If over-dispersion is ignored in such a setting, standard errors can be too small and inferential results can appear more precise than warranted.

The primary endpoint in this record is described as a continuous mean with standard deviation, not as a count outcome. The registry does not state that an over-dispersion model was used, nor does it report enough analysis detail to identify the model used for other outcomes. Over-dispersion is therefore a general statistical consideration, not a reported feature of the primary analysis.

What do the planning illustrations mean?

In general, a sample-size calculation asks how many participants would be needed under stated assumptions to detect a specified effect with a selected testing approach and power. Planning calculations are conditional on the assumptions used; they are not observations from the trial. The stated planning assumptions use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is expressed as a fraction of the observed effect.

These assumptions describe a hypothetical two-arm planning exercise, not the CELLO study’s nonrandomized single-group design. Any resulting sample-size values are planning illustrations, not evidence that the original trial had a particular power. They are not observed power. The registry record does not report the original trial’s sample-size justification or establish that these planning assumptions were part of its design.

The endpoint result needed to anchor such planning illustrations is not reported in the registry record. Accordingly, no planning result should be interpreted as an independently observed treatment effect, and no new sample-size calculation can be supported from the endpoint information in this record.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Laser Treatment")
n   <- c(65)
m   <- c(34.7)
sp  <- c(17.8)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Laser Treatment  65  34.700  17.800  30.289  39.111

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures and identifies laser success as the primary efficacy endpoint. The secondary outcomes include procedural success, minimum and maximum lumen diameters, clinical success, assisted primary and secondary patency, patients with more than 50% stenosis measured by duplex ultrasound, Rutherford Classification, and adverse events. Outcomes can address different questions and may be assessed at different times, so their results should not be treated as interchangeable.

When several outcomes or analyses are examined, multiplicity can increase the chance of at least one apparently notable finding arising by chance. In general, multiplicity procedures can control that risk, but the appropriate approach depends on the planned hierarchy and analysis strategy. The registry record does not report a multiplicity adjustment, a testing hierarchy, or a detailed statistical analysis plan. It also does not report the numerical primary result or the full set of secondary results needed to assess how findings were interpreted across outcomes.

Missing-data handling is not reported in the registry record. The record does not state how missing endpoint measurements were handled, whether any imputation was used, or how many participants had evaluable primary endpoint data. Enrollment of 65 does not establish the analysis denominator, particularly because the primary population is identified as per protocol.

The registry does not define the per-protocol criteria or report the number excluded from that population. It also does not describe an intention-to-treat analysis or a sensitivity analysis for missing data. These omissions leave uncertainty about how analysis-population selection and incomplete measurements might affect the endpoint estimate.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: coronary artery bypass graft (3.1%), congestive heart failure (3.1%), worsening coronary artery disease (1.5%), right renal artery and non-treated leg stenosis (1.5%), vessel occlusion (1.5%).

The registry lists 65 at risk for the Laser Treatment group in the serious-event listing and 11 affected in that category. It separately lists 65 at risk and 8 affected in the other-event category. These are reported counts; they should not be combined or converted into a percentage without an analysis specification. The record does not clarify the relationship between event counts and affected participants beyond the listed affected figures.

The serious-event terms listed with percentages are coronary artery bypass graft, 3.1%; congestive heart failure, 3.1%; worsening coronary artery disease, 1.5%; right renal artery and non-treated leg stenosis, 1.5%; vessel occlusion, 1.5%; and lung cancer, 1.5%. These percentages are presented as registry entries. The denominator and method for these term-specific percentages are not reported in the registry record, so they should not be reinterpreted as rates on a different denominator.

The death count is not reported in the registry record. The term list and affected counts do not establish whether an event was caused by the device or procedure. Without a comparator and fuller event definitions, timing, follow-up, and attribution details, these figures describe reported safety information rather than comparative safety effects.

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

The registry record establishes that CELLO was designed to assess safety and efficacy of the CLiRpath Photoablation Atherectomy System and that its primary efficacy endpoint was a procedural measure of stenosis reduction. It gives the endpoint definition, the assessment timing, and the per-protocol analysis population. It also identifies the single-group, nonrandomized design and lists selected adverse-event information.

The numerical primary endpoint result is not reported in the registry record. Therefore, the magnitude of the observed average reduction, its variability, and the number meeting the success threshold cannot be described from this record. No conclusion about the precision of the primary estimate is possible without those results and an uncertainty measure.

Even a reported result from this design would describe observations in the treated group; without a control group, it would not provide a randomized estimate of what would have happened under an alternative treatment or no treatment. The design also does not establish that observed outcomes were caused by the device. The registry’s safety counts and listed terms should likewise not be read as comparative risks or as proof of causation.

The primary endpoint is an immediate angiographic measure assessed during the procedure, before adjunctive therapy. It is distinct from longer-term outcomes such as patency or clinical status listed among the secondary measures. Those outcomes cannot be inferred from the primary endpoint definition, and their numerical results are not reported in the registry record.

The record is consequently informative about the study’s stated question and design, but incomplete for judging the size and precision of the primary efficacy result. It does not establish comparative effectiveness, long-term benefit, or causal safety conclusions.

14. Why This Trial Matters Statistically

This trial illustrates why endpoint definitions and study design need to be read together. Laser success is specified as a reduction in percent diameter stenosis at a defined procedural time, with angiographic core laboratory assessment. That makes clear what the investigators intended to measure, but a definition alone is not a result. Without the observed estimate and its uncertainty, readers cannot assess the magnitude or precision of the primary endpoint.

The single-group, nonrandomized design also shapes the statistical question. The record can describe outcomes among treated participants, but it has no like-for-like control group for estimating a comparative treatment effect. Randomization is useful in general because it can make treatment groups comparable in expectation; that protection is not available in a single-group design. Statistical summaries cannot compensate for the absence of a comparator.

The registry distinguishes a continuous mean endpoint from the threshold used to define success. This is a useful statistical distinction: an average describes the measurement level, while a threshold classification describes how observations fall relative to a criterion. Both can be informative, but they are not interchangeable, and the record does not provide the numerical results needed to interpret either.

Finally, this study is a reminder to separate planning calculations from observed evidence. The stated planning assumptions refer to a hypothetical two-arm calculation and are not the design of this trial. Planning illustrations do not show observed power or supply the missing primary endpoint result. Sound interpretation depends on keeping those planning assumptions, the actual study design, and the reported findings conceptually distinct.

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.

Several limitations specific to this registry record constrain interpretation. The primary endpoint result is not reported, despite the endpoint definition and assessment time being described. The record therefore lacks the observed mean, standard deviation, threshold-success count, and uncertainty estimate needed to assess the primary finding’s magnitude and precision.

The study was nonrandomized and single-group, with no masking and no comparator group. This prevents a direct like-for-like comparison and limits causal interpretation. The record does not report details of participant eligibility, the per-protocol definition, the number analyzed, exclusions, or reasons for exclusion. Although enrollment is listed as 65, that does not establish how many contributed to the primary analysis.

Missing-data methods, interim analyses, a sample-size justification, and a detailed statistical analysis plan are not reported in the registry record. Multiplicity handling is also not described despite the listing of 12 outcome measures. The available safety information does not include a reported death count, and event attribution, timing, and term-specific denominators are not described.

These limitations reflect what the registry record documents and should not be mistaken for proof that a procedure or analysis was not performed. They mean that the record alone does not permit a full evaluation of endpoint precision, analysis-population sensitivity, multiplicity, or comparative safety and efficacy.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: CELLO - CLiRpath® Excimer Laser System to Enlarge Lumen Openings — NCT00595959.
• Registry record last updated 2011-07-12; status last verified 2011-06.
• Results first posted 2009-06-19.
• 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

CELLO (NCT00595959) is a completed Phase 3, nonrandomized, single-group study of the CLiRpath Photoablation Atherectomy System for peripheral artery disease. The registry lists enrollment of 65, no masking, and Spectranetics Corporation as sponsor. The study start is 2006-11 and primary completion is 2007-04.

The primary endpoint was laser success, defined by an average reduction of at least 20% in percent diameter stenosis after laser treatment and before adjunctive therapy, assessed by angiographic core laboratory at the time of the procedure. The population was per protocol. Its numerical result is not reported in the registry record.

The record lists secondary outcomes and adverse-event information, including 11 affected in the serious-event category and 8 in the other-event category, with 65 at risk in each listing. No comparator group is described, and the record does not report the death count.