Dalteparin for Primary Venous Thromboembolism (VTE) Prophylaxis in Pancreatic Cancer Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Dalteparin for Primary Venous Thromboembolism (VTE) Prophylaxis in Pancreatic Cancer Patients (NCT00966277), a randomized phase 4 study. The primary outcome is Number of Participants With Venous Thromboembolic Events (VTE).

2. Clinical Question

This question focuses on prevention during chemotherapy, when the registry describes VTE risk as high. Including asymptomatic events means the outcome was not limited to events that brought symptoms to clinical attention: participants were also scheduled for bilateral lower-extremity ultrasound assessments. The reported outcome is a count of participants with an event, rather than a time-to-event measure or a count of all event episodes. The registry does not report a separate primary question about symptomatic events alone.

3. Trial Design

The registry describes a randomized, unmasked, phase 4 trial sponsored by M.D. Anderson Cancer Center. Participants were assigned to dalteparin or control, with the control group receiving no study drug. The dalteparin regimen was 5000 units by subcutaneous injection daily for 16 weeks. The primary outcome timeframe was also 16 weeks of treatment.

The record lists 87 participants enrolled, and the primary-outcome results list 38 participants in the dalteparin group and 37 in the control group. The registry does not explain how the enrollment count relates to the outcome denominators, or give a participant flow accounting for those counts. The record identifies the trial as completed, with a start date of 2010-04 and primary completion in 2014-09.

There is a structural inconsistency in the registry description: allocation is listed as randomized and two groups are described, but the model is listed as SINGLE GROUP. The group-specific results and the reported comparison are consistent with a two-group presentation, but the record does not explain the model label. The registry lists one outcome measure and no posted analyses. It does not report the original sample-size justification, a detailed statistical analysis plan, interim analyses, or analysis-population definitions. Those details cannot be inferred from the posted outcome counts.

The trial assessed VTE using clinical assessments and radiologic studies. The endpoint description states that participants underwent bilateral lower-extremity ultrasound every 2 months while on study, with 3 exams in total including the pre-randomization exam. The registry does not describe masking of outcome assessors, so no assumption about that process can be made.

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: Of the 87 participants enrolled on the study, only 75 were randomized. Twelve enrolling participants were screen failures or withdrew before randomization thus were excluded before assignments to groups.

Overall Study

Reasons for not completing this period:

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 Venous Thromboembolic Events (VTE), measured over 16 weeks of treatment.

The primary endpoint was the number of participants with venous thromboembolic events during 16 weeks of treatment. The registry defines VTE to include both symptomatic and asymptomatic deep venous thrombosis and pulmonary embolism, with imaging documentation required. Clinical assessments and radiologic studies were used to evaluate events, and bilateral lower-extremity ultrasound was scheduled every 2 months while participants were on study, including a pre-randomization exam as part of 3 total exams.

This endpoint is relevant to the stated prevention question because it counts participants who experienced a documented VTE during the treatment period. Including asymptomatic events can capture events that would not necessarily be identified from symptoms alone. The imaging requirement also makes documentation part of the endpoint definition. The reported measure is the number of participants with at least one qualifying event, rather than the total number of separate event episodes. The registry does not provide separate primary-outcome counts for symptomatic and asymptomatic events, or for DVT and PE individually.

The outcome is binary at the participant level: a participant either had a documented qualifying event or did not. In general, a binary endpoint allows comparison of the proportion of participants with an event in each group. The posted results report counts and group denominators, along with a recalculated risk difference and confidence interval. These results describe the observed groups during the specified treatment timeframe; they do not by themselves establish how the result would generalize to other populations or follow-up periods.

7. Results Posted in the Registry

• Group 1: Dalteparin: 5.3% (2/38) versus 24.3% (9/37) on control; risk difference -19.1 percentage points (95% CI -34.6 to -3.5), risk ratio 0.22 (0.05–0.94); unadjusted two-proportion z-test p = 0.020.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary participant-level measure: whether a participant had a documented VTE during 16 weeks of treatment. The record reports counts in each group, rather than individual participant data. For this kind of outcome, a group risk is the proportion of participants in that group who experienced the event. The posted comparison uses the control group as the reference and reports a risk difference, risk ratio, and odds ratio. These measures describe the same group contrast on different scales.

What does the risk difference express?

The risk difference is the intervention-group risk minus the control-group risk, according to the comparison's stated ordering. Its estimate is -0.191, with a 95% confidence interval from -0.346 to -0.035. A value below zero indicates that the observed event risk was lower in the dalteparin group in this comparison. A risk difference is expressed on the absolute risk scale, so its interpretation concerns the difference in event proportions rather than a relative change. The estimate is recalculated from the posted summary statistics and is not identified as a sponsor-reported analysis.

How do relative measures differ?

The risk ratio compares the group risks as a ratio; its estimate is 0.216, with a 95% confidence interval from 0.050 to 0.935. The odds ratio compares the odds of an event between groups; its estimate is 0.173, with a 95% confidence interval from 0.035 to 0.865. Both relative measures are below 1 in the reported comparison. Risk ratios and odds ratios have different definitions and should not be treated as interchangeable. With the posted counts, these measures are also recalculated, unadjusted summaries.

What does a confidence interval communicate?

In general, a confidence interval expresses the uncertainty associated with an estimate under the method used to calculate it. It gives a range of values compatible with the data and calculation, rather than a guarantee that the true effect lies in that particular interval. A narrower interval indicates greater precision on the relevant scale; a wider interval indicates less precision. The interval's endpoints are not the range of outcomes that individual participants experienced. For the risk difference, the interval is entirely below zero, while its width still allows a range of possible magnitudes.

What does the p-value add?

The reported unadjusted p-value is 0.02. In general, a p-value measures how unusual data at least as incompatible with a specified null hypothesis would be if that null hypothesis and the calculation's assumptions held. It does not measure the probability that the null is true, the probability that the result is due to chance, or the practical importance of the estimate. The registry does not post a trial analysis plan or an adjusted p-value. This p-value is part of the unadjusted recalculation from the summary counts.

What is and is not reported about the analysis?

The record lists one outcome measure and zero posted analyses. It therefore supplies endpoint counts but not a documented investigator analysis with its prespecified model, adjustment variables, or missing-data method. The randomized allocation is reported, but the model field is listed as SINGLE GROUP despite the two group descriptions. The relationship between the 87 enrolled participants and the outcome denominators is not explained. These are reporting limitations, not grounds to infer which statistical procedures the investigators planned or used.

General statistical practice distinguishes a prespecified analysis from an unadjusted calculation made from posted aggregate counts. Prespecification can determine the comparison, population, handling of missing observations, and multiplicity approach before outcomes are examined. Those details matter when interpreting a result, but they are not reported in the registry record. The recalculated comparison should consequently be interpreted as a transparent summary-statistics comparison, not as evidence that a particular unreported protocol was followed.

10. Confidence Intervals and Precision

The point estimate for the unadjusted risk difference is -0.191, and its 95% confidence interval ranges from -0.346 to -0.035. The interval is entirely below zero, but it spans a range of effect magnitudes. This means the direction of the estimated contrast is more clearly indicated than its precise size. The interval should be read as a measure of statistical uncertainty under the calculation used, not as a prediction interval for individual participants.

The relative measures also have broad intervals: the risk ratio is 0.216, with a 95% confidence interval from 0.050 to 0.935, and the odds ratio is 0.173, with a 95% confidence interval from 0.035 to 0.865. Each interval lies below 1, but the breadth indicates considerable uncertainty about the relative magnitude. The risk difference and relative measures use different scales, so their interval widths cannot be compared directly as though they measured the same quantity.

The outcome counts are 2 of 38 in the dalteparin group and 9 of 37 in the control group. The record reports 87 participants enrolled but does not explain how enrollment relates to these endpoint denominators. Without participant flow and missing-outcome information, it is difficult to assess whether the outcome counts represent all randomized participants or a defined subset. The confidence intervals quantify uncertainty in the posted comparison; they do not resolve that reporting gap or account for unreported analysis choices.

11. 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 planning figures are participants per arm, not total events. They are illustrations based on the observed effect, not the trial's original design assumptions. The planning method assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. The trial's own original sample-size assumptions are not reported in the registry record.

For planning at 100% of the observed effect, the illustration gives 54 participants per arm for 80% power and 71 participants per arm for 90% power. At 75% of the observed effect, it gives 109 participants per arm for 80% power and 145 participants per arm for 90% power. At 50% of the observed effect, it gives 271 participants per arm for 80% power and 362 participants per arm for 90% power.

In plain terms, the 80% power column is the estimated number of participants per arm needed for the stated planning scenario to have an 80% chance of detecting the specified effect under the listed assumptions. The 90% column gives the corresponding planning number for a 90% chance. These are not guarantees about a future study. Smaller effects require more participants in these illustrations because they are harder to distinguish from random variation. The figures are planning illustrations, not observed power.

12. 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 = 0.243; treatment proportion p₁ = 0.053; average p̄ = 0.148.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5021 = 0.9841.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4837 = 0.4071.
4. n = (0.9841 + 0.4071)² / (-0.1906)² = 53.3, rounded up to 54 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 <- 0.243243243243243                          # control proportion
p1 <- 0.0526315789473684                          # 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(966277)
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 = 54 (80% power), 71 (90% power)
 75% of observed effect: n per arm = 109 (80% power), 145 (90% power)
 50% of observed effect: n per arm = 271 (80% power), 362 (90% power)
power.prop.test: 53.3 
Simulated power at n = 54 per arm: 0.832 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure: the number of participants with VTE during 16 weeks of treatment. It lists zero secondary outcomes posted. The record does not report whether other outcomes were planned, whether multiple comparisons were anticipated, or whether any adjustment for multiplicity was part of the original analysis plan. With no posted secondary outcome results, the registry record does not support an assessment of a broader family of statistical tests.

The record also does not describe missing-data handling, the analysis population, or whether all randomized participants were included in the primary-outcome comparison. It reports 87 enrolled participants and outcome denominators of 38 in the dalteparin group and 37 in the control group, without a participant-flow account explaining those counts. Reasons for any unavailable outcome data, withdrawals, exclusions, or deviations from the assigned intervention are not reported in the registry record.

These details are important because the interpretation of a randomized comparison can depend on how participants are included and how missing observations are handled. In general, an analysis population specifies which participants contribute to an estimate, while a missing-data method states how unavailable measurements are treated. Neither should be inferred from the arm counts alone. The registry also does not report an interim-analysis plan, monitoring boundaries, or prespecified adjustment procedures. The absence of these details in the record does not establish that such procedures were absent from the trial; it means they are not reported in the registry record.

The allocation field identifies the study as randomized, but the model field identifies it as SINGLE GROUP despite the two group descriptions and comparison. The record does not explain this discrepancy in its design metadata. This inconsistency, together with the lack of a posted analysis plan and participant flow, limits a full audit of the intended analyses and analysis populations.

14. 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: nausea (58.8%), constipation (47.1%), vomiting (44.1%), abdominal pain (35.3%).

The adverse-event record lists 34 participants at risk and 34 affected in the dalteparin group, and 33 at risk and 33 affected in the control group. These are the serious-adverse-event group counts. The record also lists nausea at 58.8%, constipation at 47.1%, vomiting at 44.1%, and abdominal pain at 35.3% among the top serious-event terms. The registry record does not clearly report which group each listed term percentage belongs to, so the percentages should not be assigned to an arm.

The counts describe participants recorded as affected in the adverse-event reporting fields; they do not identify the nature, timing, severity grade, or duration of each participant's events. The record does not provide the event-level details needed to determine whether participants had multiple events or how events related to study treatment. Death counts are not reported in the registry record.

These safety figures should be read separately from the primary VTE endpoint. They are not a complete account of all harms, and the displayed serious-event terms do not establish a causal relationship to dalteparin. No medical conclusion follows from these counts alone.

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

The posted primary-outcome counts show 2 participants with VTE in the dalteparin group and 9 in the control group during 16 weeks of treatment. The recalculated unadjusted risk difference is -0.191, with a 95% confidence interval from -0.346 to -0.035, and the unadjusted p-value is 0.02. These statistics describe the observed groups and the uncertainty of the calculated comparison. They do not, on their own, establish a treatment effect beyond the study setting or timeframe.

The endpoint combined symptomatic and asymptomatic VTE, including DVT and PE, and required imaging documentation. The record does not give separate counts for those components. It therefore cannot establish whether the group contrast was similar for symptomatic events alone, for DVT alone, or for PE alone. The findings also concern a 16-week treatment period; longer-term outcomes are not reported in the registry record.

The trial is described as randomized, but masking is listed as none. The registry's model field says SINGLE GROUP despite the two group descriptions and comparison. The record does not report a detailed analysis plan, participant flow, missing-data methods, or definitions of the analysis populations. These omissions restrict evaluation of how the posted outcome counts relate to the full enrolled population and how the recalculated comparison relates to the investigators' intended analysis.

The results should not be interpreted as proof that dalteparin prevents VTE in every person with pancreatic cancer, nor as proof of no benefit or harm for outcomes not measured. The confidence interval expresses uncertainty about the estimated comparison, and the record contains no separate posted investigator analysis. The proper scope of the result is the observed VTE counts and unadjusted comparison for these groups, under this regimen and endpoint definition.

16. Why This Trial Matters Statistically

This trial illustrates how a clinical question can be represented as a binary endpoint and a contrast between randomized groups. The registry reports participant counts for a combined VTE outcome and the analysis can express the comparison on an absolute scale through a risk difference, as well as on relative scales through a risk ratio and odds ratio. Each scale answers a related but distinct descriptive question, so reading more than one measure can help clarify what the estimate represents.

The result also shows why precision matters alongside a point estimate and p-value. The unadjusted risk difference is -0.191, while its 95% confidence interval extends from -0.346 to -0.035. The interval indicates uncertainty in the magnitude even though it is entirely below zero. The 0.02 unadjusted p-value does not replace that information and should not be treated as a measure of clinical importance or certainty.

Another statistical lesson is the difference between posted outcome counts and a fully documented analysis. The registry includes group counts and a recalculated comparison but lists zero posted analyses. It does not provide the original analysis plan, participant flow, missing-data method, or multiplicity approach. Those omissions matter when readers assess how closely an available calculation reflects the trial's planned analysis.

Finally, the endpoint's combined definition and limited timeframe set clear boundaries on interpretation. A count that includes symptomatic and asymptomatic DVT and PE cannot by itself explain the result for any one component, and a 16-week result does not describe later outcomes. Statistical interpretation requires keeping the estimate, its uncertainty, and the scope of the measured outcome in view together.

17. 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 registry record leaves several trial-specific questions unresolved. Although it lists 87 participants enrolled, the primary-outcome groups contain 38 participants in the dalteparin arm and 37 in the control arm. No participant-flow information explains how those denominators were obtained, whether all randomized participants contributed to the endpoint, or why some enrolled participants are not represented in the posted group counts.

The record identifies randomized allocation and describes two groups, but its model field is SINGLE GROUP. It does not explain this metadata inconsistency. Masking is listed as none, and the record does not say whether outcome assessment or imaging review was masked. The endpoint required imaging documentation, making assessment procedures relevant, but those procedures beyond the listed scans are not described.

Only one outcome measure is posted, with no secondary outcomes or analyses. The original statistical analysis plan, trial-specific sample-size justification, interim analyses, missing-data methods, analysis populations, and multiplicity procedures are not reported in the registry record. The displayed comparison is an unadjusted recalculation from summary counts rather than a posted investigator analysis.

The endpoint combines symptomatic and asymptomatic VTE, DVT, and PE; component-specific counts are not reported. The timeframe is 16 weeks of treatment, and longer follow-up results are not posted. Safety reporting also has limits: the serious-event terms are listed with percentages but without clear group attribution in the record, and the death fields are not reported. These reporting gaps constrain interpretation of both efficacy and safety without implying what the unreported data might show.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Dalteparin for Primary Venous Thromboembolism (VTE) Prophylaxis in Pancreatic Cancer Patients — NCT00966277.
• Registry record last updated 2016-12-12; status last verified 2016-10.
• Results first posted 2016-12-12.
• 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.

21. Record Summary

NCT00966277 is a completed, randomized, unmasked phase 4 trial sponsored by M.D. Anderson Cancer Center. It enrolled 87 participants with pancreatic cancer receiving chemotherapy. The intervention was dalteparin 5000 units by subcutaneous injection daily for 16 weeks; the control group received no study drug.

The primary outcome was the number of participants with VTE during 16 weeks of treatment, including symptomatic and asymptomatic DVT and PE. The registry reports 2 participants with VTE among 38 in the dalteparin group and 9 among 37 in the control group. An unadjusted recalculated comparison reports a risk difference of -0.191, with a 95% confidence interval from -0.346 to -0.035 and p = 0.02.

The record lists one outcome measure and zero posted analyses. It does not report the original statistical analysis plan, participant flow, or missing-data methods. Its two-group randomized description also sits alongside a SINGLE GROUP model label.