Metabolism of NNK in Japanese Americans: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Metabolism of NNK in Japanese Americans (NCT04228952), a registered phase not stated study. The primary outcome is The Ratio of D4-hydroxy Acid to D4- NNAL (an Estimate if NNK Alpha Hydroxylation).

2. Clinical Question

The study’s stated purpose is to explore whether individual differences in metabolism of a tobacco-specific lung carcinogen may contribute to variation in lung cancer risk between ethnic or racial groups. The described endpoint assesses metabolism; it is not a measure of lung cancer incidence or risk. The record describes Japanese American smokers and does not provide a comparison with another ethnic or racial group.

3. Trial Design

The registry lists this as a completed clinical trial with enrollment of 16 and the condition of smoking. Its stated title is “Metabolism of NNK in Japanese Americans.” The sponsor is Masonic Cancer Center, University of Minnesota. The registry dates the study start as 2020-09-01 and primary completion as 2021-10-15.

The brief description calls the study a 10 day clinical trial. Participants were to smoke a cigarette containing deuterium-labeled NNK, and the study cigarette was to be smoked for 7 days. The primary endpoint timeframe is also listed as 7 days. The record does not describe additional visits, specimen collection schedules, or the precise timing of endpoint measurement.

The intervention is described as modified Natural American Spirit-Tan or Green cigarettes injected with labeled NNK. The listed groups are smokers with very low or no CYP2A6 activity and smokers with high CYP2A6 activity. The activity definitions use the trans-3-hydroxycotinine:cotinine ratio: less than 0.6 for the very low or no activity group and greater than 3.0 for the high activity group. The record does not explain how participants with values between those thresholds were treated.

The registry explicitly cautions that this is not a randomized comparison and that allocation is not stated. It also notes that the arms are not a like-for-like control comparison. The description does not establish whether the cigarettes differed in anything other than the labeled NNK feature, or whether other aspects of participants’ smoking behavior were controlled. Randomization procedures, masking, and a separate control intervention 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.

Overall Study

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 The Ratio of D4-hydroxy Acid to D4- NNAL (an Estimate if NNK Alpha Hydroxylation), measured over 7 days.

The primary endpoint is the ratio of D4-hydroxy acid to D4-NNAL, described as an estimate of NNK alpha hydroxylation. The deuterium label in the study cigarette allows the named metabolites to be associated with the labeled NNK exposure, according to the study description. The endpoint is a continuous measure, and the registry specifies that the intended summary is a mean with a standard deviation.

As a general statistical matter, a continuous metabolic measure can describe variation in a biochemical response across participants and can be compared between groups using a difference in means. The direction and size of such a difference would depend on the observed values. The registry record does not report group means, standard deviations, a difference estimate, or uncertainty around that estimate, so those features cannot be interpreted for this trial.

The endpoint is intended to characterize metabolism during the stated 7 days, not to measure a clinical outcome such as lung cancer. Its interpretation depends on the meaning and measurement of the ratio, details that are not fully specified in the registry. The outcome description also contains a contrast of “null versus average CYP2A6 activity,” while the named arms are very low or no activity and high activity. That inconsistency leaves the exact group contrast unclear. The record does not explain why this particular ratio was selected over other possible metabolic measures.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary measure as continuous and specifies a mean and standard deviation as its summary statistics. A mean describes the central value of a set of measurements. A standard deviation describes how spread out individual measurements are around that mean. These summaries address different features: the mean describes the group average, while the standard deviation describes variation among observations. Neither is reported for the primary endpoint in the registry record.

What would a difference in means describe?

For a continuous endpoint, a difference in means expresses how far apart the two group averages are on the endpoint’s measurement scale. Its interpretation requires knowing which group is subtracted from which, as well as the observed mean in each group. The registry calls for a difference in means but does not report the calculation’s result or clearly define the order of subtraction. The inconsistency between the endpoint’s “null versus average CYP2A6 activity” wording and the named groups adds uncertainty about the intended contrast.

A mean difference is an estimate, not a complete account of evidence. Its uncertainty depends on the observed data and on the analysis method. A confidence interval is a general way to express that uncertainty: it gives a range of values compatible with the data under the stated method. A narrow interval generally indicates greater precision than a wide one, but interpretation also depends on the endpoint and study question. No interval is listed for this endpoint, and no alternative uncertainty measure is reported.

What can a p-value establish?

As a general statistical concept, a p-value describes how unusual data at least as incompatible with a specified null model would be if that model and the assumptions used for the test held. It is not the probability that the null hypothesis is true, and it does not quantify the size or clinical importance of an effect. The registry record does not list a p-value or identify a test for the primary endpoint. A significance threshold or inferential plan is not reported in the registry record.

Why does the group structure matter?

The activity-defined groups are not described as randomized arms. The record says allocation is not stated and cautions that the arms are not a like-for-like control comparison. In general, randomization can help balance measured and unmeasured participant characteristics across groups, whereas a nonrandomized group comparison may retain differences that influence the measured outcome. This does not show that any particular bias occurred in this study; it means the registry record does not establish that group differences can be attributed only to CYP2A6 activity.

Adjustment can sometimes address measured differences, but the record does not describe covariate adjustment or any model. It does not report the participant characteristics used in an analysis, if any. The registry also does not state how the thresholds defining the activity groups were chosen or how observations between the stated thresholds were handled. These omissions limit the ability to evaluate how the group comparison was constructed.

How should the planning illustrations be read?

The registry describes planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. For continuous outcomes, the illustrations are expressed as participants per arm. No numerical illustration values or fraction values are reported in the record, and no calculation can be interpreted from the endpoint results because those results are not posted.

As a general concept, a sample-size illustration estimates the number of participants that a future study might require under stated assumptions. It is not an observed effect, an outcome result, or evidence that the current trial had a particular probability of detecting a difference. It should not be called observed power. The registry explicitly characterizes these illustrations as planning calculations rather than the trial’s own design. Its assumptions do not establish that the trial’s original enrollment was selected by this method.

Over-dispersion is a general issue when observed variation exceeds what a statistical model assumes. In that situation, standard errors may be underestimated and uncertainty may appear too small unless the analysis accounts for the extra variation. The registry specifies a continuous endpoint summarized by a mean and standard deviation; it does not identify a count model or report evidence of over-dispersion. Therefore, over-dispersion is not a documented feature of this analysis. More generally, the choice of model should match the endpoint’s distribution and measurement properties, but those details are not described.

The record lists one outcome measure and no analyses. This does not reveal which statistical procedures were conducted or whether any analysis occurred outside the registry entry. The registry does not report a statistical analysis plan, interim analyses, or a sample-size justification. Those details should not be inferred from the planning assumptions or from the completed status.

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("Smokers With Very Low or no CYP2A6 Activity", "Smokers With High CYP2A6 Activity")
n   <- c(8, 8)
m   <- c(0.133, 0.175)
sp  <- c(0.096, 0.066)
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  Smokers With Very Low or no CYP2A6 Activity  8  0.133  0.096  0.053  0.213
CARM  Smokers With High CYP2A6 Activity  8  0.175  0.066  0.120  0.230

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, the ratio of D4-hydroxy acid to D4-NNAL, as the primary endpoint. It lists no analyses. This entry does not establish whether additional outcomes were examined, whether multiple comparisons were made, or how any multiplicity was handled. A multiplicity adjustment or rationale is not reported in the registry record.

As a general statistical matter, testing several outcomes, time points, or group contrasts can increase the chance of obtaining an apparently unusual result by chance if each test is interpreted separately. Prespecified priorities and appropriate methods can help make such analyses more interpretable. The record does not state whether the primary endpoint or contrast was prespecified in a protocol, and it does not report a strategy for multiple testing. The absence of that information is not evidence that multiplicity occurred or that it was ignored.

Missing-data methods and analysis populations are also not reported in the registry record. The endpoint-specific number of measurements, reasons for missing measurements, rules for excluding observations, and any imputation approach are not stated. It is therefore not possible to determine from the registry which participants were included in the endpoint analysis or how incomplete observations were handled. The enrollment and the safety denominators do not resolve those questions.

The registry does not identify an intention-to-treat, per-protocol, or other analysis population. Those labels should not be inferred merely from the study’s completed status or the group descriptions. The statistical analysis plan, including handling of missing data and analysis populations, is not reported in the registry record.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The safety record lists zero serious adverse events and zero other adverse events in the group of smokers with very low or no CYP2A6 activity. It also lists zero serious adverse events and zero other adverse events in the group of smokers with high CYP2A6 activity. For each group, the record lists 8 participants at risk for serious adverse events and 8 at risk for other adverse events. It lists zero deaths in each group.

These are the registry’s recorded counts. They do not provide detail about how adverse events were defined, collected, graded, or attributed, or the period over which they were assessed. The record does not clarify whether events were captured for every participant throughout the study. Zero recorded events should therefore be read as a feature of the posted safety data, not as proof that no symptoms or events occurred.

The counts do not describe the primary metabolic endpoint and cannot answer the study’s main statistical question. They also do not provide a comparative safety estimate or uncertainty interval. The registry record does not report a safety analysis plan or further detail about adverse-event ascertainment.

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

The record describes a small completed study focused on NNK metabolism in Japanese American smokers. Its primary measure is a ratio intended to estimate NNK alpha hydroxylation, compared across groups defined by CYP2A6 activity. The study question concerns a metabolic measure during the stated exposure period, rather than a clinical outcome such as lung cancer.

The posted results do not include the primary endpoint’s observed means, standard deviations, difference in means, or inferential statistics. As a result, the record does not show whether the metabolic measure was higher in one group, lower in one group, or similar across groups. It also does not show how precisely any difference was estimated. The absence of a reported estimate should not be interpreted as evidence that there was no difference.

The group comparison has limitations that affect interpretation. The registry says allocation is not stated and the arms are not a like-for-like control comparison. The endpoint wording also describes a contrast of “null versus average CYP2A6 activity,” which does not correspond clearly to the named groups of very low or no activity and high activity. The record does not report an adjusted analysis that might clarify how participant differences were handled.

The study’s stated rationale connects variation in NNK metabolism with variation in lung cancer risk across individuals and ethnic or racial groups. However, the reported endpoint is a metabolic estimate, and the registry does not report lung cancer outcomes or a comparison across ethnic or racial groups. A metabolic result, even if available, would not by itself establish a difference in lung cancer risk.

The safety record lists no serious adverse events, other adverse events, or deaths in either group, with 8 participants at risk listed for each safety category in each group. These counts are limited to the entries in the registry and do not replace detailed information about event collection or duration. Overall, the record establishes the study’s stated question and design features, but not the primary outcome findings needed to assess the metabolic comparison.

14. Why This Trial Matters Statistically

This study illustrates a distinction between measuring a biological process and measuring a clinical outcome. The primary endpoint is a ratio intended to estimate NNK alpha hydroxylation. Such a measure can be relevant to a mechanistic question about metabolism, but it is not itself a measure of disease occurrence. Keeping that distinction clear prevents a biochemical comparison from being treated as a direct estimate of lung cancer risk.

It also highlights the importance of a well-defined contrast. The named groups are based on very low or no CYP2A6 activity and high CYP2A6 activity, while the endpoint description refers to “null versus average CYP2A6 activity.” When the population labels and stated comparison do not align, readers cannot be certain which contrast the intended estimate represents. Clear group definitions and a consistent endpoint description are essential for interpreting a mean difference.

The registry’s caution that this is not a like-for-like control comparison also matters statistically. An association between group membership and a metabolic measurement may be affected by participant characteristics or other differences between groups. Randomization and adjustment are possible ways to address particular sources of imbalance, but the registry does not describe randomization or an adjusted analysis. Statistical interpretation should therefore stay within the design details that are actually recorded.

Finally, a study record can describe a question and endpoint without making the results interpretable. Means, variability, an estimate of the between-group contrast, and uncertainty are needed to assess the magnitude and precision of a continuous outcome comparison. Those results are not reported in the registry record. This case demonstrates why completion status, a stated endpoint, and safety counts are not substitutes for posted efficacy or biomarker estimates.

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 main limitation for interpreting this trial is that the registry record does not report the primary outcome results. Without endpoint values or an estimated group contrast, the metabolic comparison cannot be evaluated for direction, magnitude, or precision. The record also does not report endpoint-specific analysis counts, so the enrollment figure does not establish how much information contributed to the primary analysis.

The endpoint’s group contrast is described inconsistently. The primary outcome description refers to “null versus average CYP2A6 activity,” whereas the arm descriptions identify very low or no activity and high activity. The record does not resolve whether the intended comparison was between those named groups or another contrast. The thresholds are stated, but the handling of participants whose activity values fall between the thresholds is not reported.

The record does not state allocation, and it explicitly cautions that the arms are not a like-for-like control comparison. Randomization, masking, participant characteristics relevant to the comparison, and adjustment methods are not described. Thus, even if endpoint estimates were available, the registry would not provide enough information to assess whether differences between groups could be separated from other group differences.

Details about the measurement and analysis are also limited. The record does not describe the collection and assay procedures, endpoint distribution, missing-data handling, exclusions, analysis populations, or statistical model. It does not report a statistical analysis plan, multiplicity strategy, interim analyses, or sample-size justification. The planning assumptions listed in the record are not a substitute for those details and are identified as illustrations rather than the trial’s design.

The safety entries list zero events, but the registry does not provide event definitions, ascertainment details, or a clear assessment period for those counts. In addition, the outcome is a metabolic estimate rather than a clinical disease outcome. The record therefore cannot establish effects on lung cancer risk or support comparisons across ethnic or racial groups.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Metabolism of NNK in Japanese Americans — NCT04228952.
• Registry record last updated 2025-08-01; status last verified 2025-07.
• Results first posted 2025-08-01.
• 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 lists NCT04228952 as a completed study titled “Metabolism of NNK in Japanese Americans,” sponsored by Masonic Cancer Center, University of Minnesota. Enrollment is listed as 16. The study description concerns Japanese American smokers who smoke a cigarette containing deuterium-labeled NNK, with study-cigarette smoking described for 7 days during a 10 day trial.

The primary endpoint is the ratio of D4-hydroxy acid to D4-NNAL, described as an estimate of NNK alpha hydroxylation and summarized as a mean with a standard deviation. The named groups are based on CYP2A6 activity. The registry cautions that the comparison is not randomized, allocation is not stated, and the arms are not a like-for-like control comparison.

Numerical primary endpoint results and inferential statistics are not reported in the registry record. The safety entries list zero serious adverse events, zero other adverse events, and zero deaths in each group. Missing-data handling, analysis populations, and the statistical analysis plan are not reported.