Study Comparing Two Types of Ports in Patients With Cancer Receiving Intravenous Chemotherapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study Comparing Two Types of Ports in Patients With Cancer Receiving Intravenous Chemotherapy (NCT00607880), a randomized phase 2 study. The primary outcome is Port Failure Within 12 Months of Port Insertion.

2. Clinical Question

3. Trial Design

This was a randomized, double-masked, parallel-group phase 2 study sponsored by Mayo Clinic. Its official title describes a prospective comparison of the Vortex Implantable Access Port and the BardPort Implantable Port in patients with cancer receiving adjuvant intravenous chemotherapy. Participants assigned to either port were to receive standard chemotherapy after port insertion. The registry record lists 100 participants enrolled and the study status as completed.

The study began in 2004-06, with primary completion recorded as 2009-03. The trial compared two port types rather than comparing a port with no port or comparing chemotherapy regimens. The registry record identifies vascular access device placement as the intervention. Although the study is described as double-masked, it does not report which people were masked or how masking was maintained.

The primary endpoint results use 31 participants in the Standard Access Port group and 29 in the Vortex group. This is a narrower analysis population than the enrollment total. The endpoint description specifies that participants with failure and those followed for 12 months without failure were included; the registry record does not explain why other enrolled participants are not represented in these primary denominators. The secondary outcome results use different denominators, as described in their registry entries. The reason for those differences is not reported in the registry record.

The registry record lists three secondary outcomes: death from all causes, port removal for reasons other than infection or occlusion within 12 months, and termination of use of the indwelling port at 12 months. Numeric results are available for death and termination of port use. A numeric result for port removal is not reported in the registry record. The record lists four outcome measures overall but no reported analyses. It does not report the original statistical plan or the assumptions used to design the trial.

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: One patient in the Standard Access Port group was unable to have the port placed due to chronic left internal jugular occlusion and was excluded from the analyses.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Patients with port failure within 12 months and patients that were followed 12 months without port failure were included in this analysis.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: All 100 patients accrued to participate in this study were included in the baseline population analysis.

6. Primary Endpoint

The registry lists the primary outcome as Port Failure Within 12 Months of Port Insertion, measured over Up to 12 months from port insertion.

The primary endpoint is the proportion of participants with port failure within 12 months of port insertion. Failure combines port malfunction due to partial or total occlusion with any infection related to the port. A participant meeting either part of this definition counts as having the composite outcome; the registry record does not report the components separately.

The denominator is defined as participants who had a reported failure within 12 months plus participants followed for 12 months without failure. Thus, this proportion describes failure among the stated analysis population, rather than among everyone enrolled in the trial. Participants whose outcome status did not meet either stated denominator condition are not described in this endpoint definition.

A composite can capture more than one clinically relevant way a device may fail, and can provide a single outcome for comparing groups. Its interpretation depends on the components: a difference in the composite would not by itself show which component contributed to that pattern. In this trial, the arm-specific proportions were 16.1% for the Standard Access Port and 13.8% for the Vortex Implantable Access Port. The registry record reports 95% confidence intervals for each proportion. It does not report separate estimates for occlusion-related malfunction and infection, so the relative contribution of those events cannot be assessed from these results.

7. Results Posted in the Registry

• Vortex Implantable Access Port: 13.8% (4/29) versus 16.1% (5/31) on control; risk difference -2.3 percentage points (95% CI -20.4 to 15.7), risk ratio 0.86 (0.25–2.88); unadjusted two-proportion z-test p = 0.800.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Death From All Causes

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Vortex Implantable Access Port: 12.0% (6/50) versus 18.4% (9/49) on control; risk difference -6.4 percentage points (95% CI -20.5 to 7.7), risk ratio 0.65 (0.25–1.70); unadjusted two-proportion z-test p = 0.377.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Vortex Implantable Access Port and the control. The interval gives the range of effects that remain compatible with the data.

Termination of Use of the Indwelling Port at 12 Months After Port Insertion

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Vortex Implantable Access Port: 62.0% (31/50) versus 63.3% (31/49) on control; risk difference -1.3 percentage points (95% CI -20.3 to 17.8), risk ratio 0.98 (0.72–1.33); unadjusted two-proportion z-test p = 0.896.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Vortex Implantable Access Port and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes provide a broader view of events recorded during follow-up, but they do not materially settle the uncertainty in the primary composite comparison. The posted secondary results include all-cause death and termination of use of the indwelling port. The registry record also lists port removal for reasons other than infection or occlusion, but a numeric result for that outcome is not reported in the registry record.

For the secondary outcomes with numeric comparisons, the unadjusted p values are 0.377 for all-cause death and 0.896 for termination of port use. Their comparison intervals include values in either direction. These results do not demonstrate a clear between-group difference, but they also do not establish equivalence or rule out differences that the data estimate imprecisely. The secondary endpoints are distinct from the primary composite: death and port-use termination do not identify the specific causes of port failure.

These outcomes are most useful as descriptive context rather than as independent confirmation of the primary result. The registry record does not report a multiplicity plan, such as a method for controlling the chance of false-positive findings across multiple outcomes. When several outcomes are examined, an unadjusted result carries less confirmatory weight than a primary analysis defined in advance and interpreted within a reported analysis plan. No reported analyses are listed in the registry record, and the reasons for the varying endpoint denominators are not given. Together, these limitations argue for caution when comparing the secondary results or treating them as a coherent test of a single hypothesis.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Death From All Causes
• Port Removal for Any Reason Other Than Infection or Occlusion Within 12 Months After Port Insertion
• Termination of Use of the Indwelling Port at 12 Months After Port Insertion

9. Statistical Interpretation

10. Statistical Methods Explained

What kind of outcome is this? The primary endpoint is binary at the participant level: each included participant either had a port failure within 12 months or was followed for 12 months without failure. A binary outcome can be summarized as a count and a proportion in each group. Here, the reported proportions are 16.1% for the Standard Access Port and 13.8% for the Vortex Implantable Access Port. The denominator definition matters: these are not proportions calculated from the full enrollment total, but from the endpoint population specified in the registry record.

The endpoint is also a composite. It combines malfunction due to partial or total occlusion with any port-related infection. Combining events can make a single summary measure that reflects more than one type of failure. However, the composite result cannot reveal whether one component occurred more often than another. Component-specific event counts and comparisons are not reported in the registry record.

How should the group proportions be read? Each proportion describes the observed share of analyzed participants in one group who experienced the composite failure outcome by the stated time. The event counts were 5 of 31 in the standard-port group and 4 of 29 in the Vortex group. A proportion is an estimate for the broader population from which trial participants might be drawn, not a guarantee of the proportion that would be seen in another group of patients. The confidence interval conveys uncertainty in that estimate.

What does the comparison measure? A risk difference expresses the difference between the groups’ event proportions on the same absolute scale. A risk ratio compares the proportions as a relative quantity, while an odds ratio compares the odds of the event. These are different ways to describe a binary-outcome contrast; each has its own scale and interpretation. The registry record lists a risk-difference comparison and also contains ratio estimates. The numeric ratio estimates are not repeated because they are not needed to interpret the main pattern. No adjustment variables are reported for these comparisons, so they should be read as unadjusted rather than as adjusted for participant characteristics.

The unadjusted p value for the primary comparison is 0.8. In general, a p value describes how compatible the observed data are with a specified null hypothesis under the assumptions of the test. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. A value of 0.8 does not prove that the groups are identical. The registry record does not identify a sponsor-reported test or provide a detailed primary analysis plan; it lists no reported analyses.

Why are confidence intervals useful? A confidence interval gives a range of values compatible with the observed data under the method used to calculate it. In repeated use of the same method, intervals constructed in this way have a stated coverage property. An interval is not a probability statement about a particular fixed effect after the data are observed. For the arm-specific proportions, the reported 95% intervals are broad. For the comparison, the reported interval extends to values favoring either group. This is a signal of imprecision, not evidence that every value in the interval is equally likely or equally important.

General statistical interpretation also distinguishes statistical significance from practical importance. A small p value alone would not establish that a difference matters clinically; conversely, a non-small p value does not rule out a meaningful difference if the estimate is imprecise. The registry record does not report a threshold for a clinically important difference, so these results cannot be judged against a prespecified importance criterion.

Why can the denominators differ? The primary endpoint population is explicitly limited to participants with failure or those followed for 12 months without failure. Other outcome entries use different denominators. A denominator can vary across outcomes when availability or definitions differ, but the reason for the differences in this trial is not reported in the registry record. It would be inappropriate to assume that all enrolled participants were included in every outcome analysis or to infer how unobserved outcomes were handled.

The registry record identifies randomization and double masking, but does not describe the randomization procedure, allocation concealment, the masked parties, or methods for maintaining masking. It also does not describe model assumptions for the trial’s original analysis, adjustment for covariates, a plan for missing outcomes, or any interim analysis. These absences limit the ability to assess the analysis beyond the posted counts and summary statistics. General statistical concepts explain what the reported summaries mean; they do not fill in those unreported study procedures.

11. Confidence Intervals and Precision

Precision concerns how narrowly the data estimate an outcome or a comparison. For the primary endpoint, the 95% confidence interval for the Standard Access Port proportion runs from 3.2% to 29.0%, and the interval for the Vortex proportion runs from 1.2% to 26.4%. Both intervals are wide relative to their point estimates. This indicates that the trial data leave considerable uncertainty about the failure proportion in each group.

The primary comparison also has an interval that spans values in both directions. It is therefore compatible with a lower failure proportion in the Vortex group and with a higher failure proportion in that group. The interval does not isolate a single direction of effect. The unadjusted p value of 0.8 is consistent with the lack of a clear statistical separation, but it should not be interpreted as proof of no difference.

Small analysis groups contribute to uncertainty: the primary endpoint includes 31 participants in the standard-port group and 29 in the Vortex group. Only 5 and 4 failures, respectively, were observed. With relatively few events, estimates can be sensitive to the observed event counts, and confidence intervals can remain broad. Randomization supports a comparative design, but it does not remove uncertainty from limited outcome information.

Precision is also affected by the endpoint definition and analysis population. The primary result concerns a composite and excludes participants not covered by the stated denominator rule. The registry record does not report component-specific intervals, reasons for the denominator differences, or a missing-data analysis. As a result, the available intervals quantify uncertainty for the reported summaries, not uncertainty about every possible outcome definition or analysis population.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations based on the observed effect, not the trial’s original design calculations. The registry record does not report the original sample-size justification or design assumptions. The listed planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect defined as a stated fraction of the observed effect. For these binary outcomes, the figures refer to participants per arm, not total events. The time-to-event convention described in the record does not apply to these outcomes.

The 80% power column indicates the number of participants per arm estimated to give an 80% chance of detecting the assumed effect under those planning assumptions, if that effect and the calculation assumptions were correct. The 90% column expresses the analogous planning target at 90% power. Higher target power generally requires a larger planned sample. These calculations are conditional planning illustrations; they are not observed power.

Rows using a smaller fraction of the observed effect assume a more modest difference between groups. Smaller effects are harder to distinguish from sampling variation, so they require more participants per arm to reach the same power target. The resulting figures should not be read as recommendations or as evidence that the trial was designed to detect those effects. They are sensitive to the observed effect used as the starting point, which itself is uncertain, especially when the outcome groups and event counts are limited.

For the primary endpoint, the planning calculation uses a binary outcome and the observed comparison. It does not account for unreported design features, potential missing outcomes, or any considerations not included in the stated planning assumptions. The original trial’s intended effect size, sample-size rationale, and target power are not reported in the registry record.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.161; treatment proportion p₁ = 0.138; average p̄ = 0.150.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5044 = 0.9887.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5042 = 0.4243.
4. n = (0.9887 + 0.4243)² / (-0.0234)² = 3,659.0, rounded up to 3,659 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.161290322580645                          # control proportion
p1 <- 0.137931034482759                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(607880)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 3,659 (80% power), 4,898 (90% power)
 75% of observed effect: n per arm = 6,610 (80% power), 8,849 (90% power)
 50% of observed effect: n per arm = 15,107 (80% power), 20,223 (90% power)
power.prop.test: 3659 
Simulated power at n = 3,659 per arm: 0.804 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The record lists a primary endpoint and several secondary outcomes, but a plan for handling multiple comparisons is not reported in the registry record. When investigators examine multiple outcomes, the chance of at least one apparently notable result can increase. General approaches include designating a primary test in advance, using a prespecified testing sequence, or adjusting inference across outcomes. The record does not say whether any such approach was used. The posted secondary comparisons are unadjusted, so they should be interpreted as exploratory rather than as a family of confirmatory tests.

The registry record lists no reported analyses. It does not describe the original statistical analysis plan, the statistical tests used by the investigators, adjustment for baseline characteristics, subgroup analyses, interim analyses, or stopping rules. These details cannot be inferred from the randomized, double-masked, parallel design or from the posted summary statistics.

The primary endpoint population is described as participants with failure within 12 months and participants followed for 12 months without failure. The registry record does not explain the status or handling of participants outside those categories. It does not report an intention-to-treat or per-protocol analysis population, a missing-data method, or sensitivity analyses addressing missing outcomes. The primary endpoint denominators are smaller than total enrollment, but the reasons are not reported in the registry record; no cause should be assigned to that difference.

Different secondary outcome entries also use different denominators, and the registry record does not explain why. The all-cause death and port-use termination results are posted, but a numeric result for port removal is not reported in the registry record. Without analysis-population definitions and missing-data methods for each endpoint, it is difficult to determine how representative each result is of all randomized participants. These reporting gaps limit assessment of multiplicity, completeness, and the robustness of the comparisons.

15. 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

Serious events with the highest arm-level rate: vascular - other (8.2%), infection with unknown anc: blood (4.1%).

The serious adverse event summary reports 5 affected participants among 49 at risk in the Standard Access Port group and 4 among 50 at risk in the Vortex group. The record also lists serious-event terms including “Vascular - Other” at 8.2% and “Infection with unknown ANC: Blood” at 4.1%. The registry record does not clarify whether participants could contribute to more than one term, so the term percentages should not be added or treated as mutually exclusive categories.

No participants were reported with other adverse events in either group: 0 of 49 in the standard-port group and 0 of 50 in the Vortex group. Death counts in this adverse-event summary are not reported. Separately, the secondary all-cause death outcome gives participant counts for follow-up; that endpoint is distinct from the adverse-event field. These summaries are descriptive and do not by themselves establish that an event was caused by a port or demonstrate a comparative safety difference. The record does not report a detailed safety analysis plan.

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

The posted primary results describe the proportion of analyzed participants who experienced a composite port failure by 12 months. The observed proportions were 16.1% for the Standard Access Port and 13.8% for the Vortex Implantable Access Port. The unadjusted comparison is imprecise: its uncertainty includes possibilities favoring either group, and the p value is 0.8. The results therefore do not identify a clear difference, but they do not show that the ports are equivalent.

Equivalence requires a prespecified margin defining how much difference would be considered acceptably small, together with an analysis designed to assess that margin. The registry record does not report an equivalence or non-inferiority objective or margin. A failure to find a statistically clear difference is not the same as demonstrating equivalence. Nor does a point estimate alone establish the direction or importance of an underlying effect.

The primary outcome is a composite of malfunction and infection. The posted overall result does not reveal how many failures were due to each component. It also applies to the analysis population defined in the registry record, not automatically to every enrolled participant. The record does not provide enough information to assess how participants outside the stated primary denominator were handled or why outcome denominators vary.

Randomization and masking are important design features, but the record does not describe implementation details or the full statistical plan. The outcome summaries can be read as evidence about what was observed in the analyzed groups; they cannot answer unreported questions about component-specific effects, missing outcomes, or prespecified clinical importance. These findings are statistical descriptions of this trial’s posted data, not medical advice and not a general claim about port performance in every population or setting.

17. Why This Trial Matters Statistically

This trial illustrates the distinction between a point estimate and the precision of the evidence around it. The observed primary proportions are close in the posted summaries, but the confidence intervals are broad and the comparison remains compatible with effects in either direction. A reader who focuses only on the two percentages or the p value could miss the amount of uncertainty in the data.

It also shows why the analysis population and endpoint definition matter. The primary result is based on participants with failure or with 12 months of follow-up without failure, rather than the full enrollment total. The composite includes two kinds of port-related events, but component-specific results are not reported. Those details shape what can reasonably be concluded from the comparison.

Finally, the record supports only a limited assessment of the statistical methods. It identifies a randomized, double-masked design and posts outcome summaries, but it does not report the original analysis plan, missing-data handling, multiplicity procedures, or original sample-size justification. Planning illustrations based on the observed effect cannot substitute for that design rationale. The case is a useful reminder that interpretation depends not only on estimates and p values, but also on prespecified methods, complete population definitions, and transparent reporting.

18. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

Several limitations are specific to the available record. The primary analysis includes 31 participants in the Standard Access Port group and 29 in the Vortex group, while enrollment was 100. The endpoint definition restricts the denominator to participants with failure or with 12 months of follow-up without failure. The registry record does not explain the remaining difference or report how participants not included in that denominator were handled. This limits assessment of completeness and potential selection effects.

The primary endpoint is a composite, but the component results are not reported separately. It is therefore not possible to determine whether occlusion-related malfunction, infection, or both account for the observed failures. The comparison estimates are imprecise, with wide arm-specific confidence intervals and few observed failures. The record does not identify a prespecified clinically important difference against which to judge the size of the estimate.

Analysis details are also limited. The registry record does not report the original statistical plan, missing-data methods, adjustment for multiple outcomes, allocation concealment procedures, or which parties were masked. It lists three secondary outcomes, but a numeric port-removal result is not reported in the registry record. The reason for differing endpoint denominators is not reported. These gaps do not change the posted counts, but they restrict how fully the robustness and scope of the findings can be evaluated.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Study Comparing Two Types of Ports in Patients With Cancer Receiving Intravenous Chemotherapy — NCT00607880.
• Registry record last updated 2014-05-09; status last verified 2014-04.
• Results first posted 2014-05-09.
• 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.

22. Record Summary

The registry record describes a completed randomized, double-masked, parallel phase 2 comparison of the Vortex Implantable Access Port and a standard access port in patients with cancer receiving intravenous chemotherapy. Enrollment was 100. The primary endpoint was port failure within 12 months, defined as occlusion-related malfunction or port-related infection.

The primary analysis reported failure proportions of 16.1% for the standard port and 13.8% for the Vortex port, with an unadjusted p value of 0.8 and wide arm-specific confidence intervals. The analysis population was smaller than total enrollment, and the reason is not reported. Numeric secondary results are available for all-cause death and termination of port use; a numeric port-removal result is not reported. The registry record does not report the original analysis plan, missing-data methods, or multiplicity procedures.