To the Editor:
We read with great interest the recent article by Sangchan et al.
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The authors concluded that endoscopic biliary drainage with a self-expandable metal stent (SEMS) provides better adequacy of drainage and longer survival compared with the plastic stent (PS) in patients with unresectable complex hilar cholangiocarcinoma. It is an interesting study. Nevertheless, several issues seem worthy of comment.First, as noted in this article, the difference in patient age distribution between the SEMS and PS groups was statistically significant (P = .013). It leads to an imbalance between treatment groups. However, ignoring the imbalances in continuous covariates causes the loss of power in randomized, controlled trials.
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Moreover, an extreme degree of imbalance in baseline variables prognostic of response variables may lead to a misleadingly significant estimate of treatment effect. It is suggested that covariate adaptive allocation is often adopted in clinical trials to maintain the balance of baseline covariates.3
Second, full reporting of any deviations from random allocation and missing response is essential in the assessment of the necessity and appropriateness of an intention-to-treat approach, as emphasized in the CONSORT guidelines on the reporting of randomized, controlled trials.
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Unfortunately, the authors did not report deviations from randomized allocation and missing response. Furthermore, the potential effect of missing response was not discussed, which is important for intention-to-treat analysis.5
Finally, radiotherapy is known to improve patient prognosis and the patency of uncovered metal stents in patients with locally advanced hilar cholangiocarcinoma.
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The authors should consider this factor, which may influence the survival of patients in the SEMS group.To summarize, this study suggests that the endoscopic SEMS was better than the PS in unresectable complex hilar cholangiocarcinoma with regard to adequacy of drainage and patient survival. Well-designed, unbiased prospective studies based on a larger sample size are still needed. We believe that our remarks will contribute to more accurate elaboration of the results presented by Sangchan et al.
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References
- Efficacy of metal and plastic stents in unresectable complex hilar cholangiocarcinoma: a randomized controlled trial.Gastrointest Endosc. 2012; 76: 93-99
- Quantifying the cost in power of ignoring continuous covariate imbalances in clinical trial randomization.Contemp Clin Trials. 2011; 32: 250-259
- Sequential treatment assignment with balancing for prognostic factors in the controlled clinical trial.Biometrics. 1975; 31: 103-115
- Improving the quality of reporting of randomized controlled trials.JAMA. 1996; 276: 637-639
- What is meant by intention to treat analysis?.BMJ. 1999; 319: 670-674
- Clinical benefit of radiation therapy and metallic stenting for unresectable hilar cholangiocarcinoma.World J Gastroenterol. 2012; 18: 2364-2370
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© 2013 American Society for Gastrointestinal Endoscopy. Published by Elsevier Inc. All rights reserved.
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- Efficacy of metal and plastic stents in unresectable complex hilar cholangiocarcinoma: a randomized controlled trialGastrointestinal EndoscopyVol. 76Issue 1
- PreviewEndoscopic biliary stent drainage is effective in the palliative treatment of patients with hilar cholangiocarcinoma (HCA). However, no randomized controlled trial comparing the efficacy of the self-expandable metal stent (SEMS) and the plastic stent (PS) in patients with unresectable complex HCA is available.
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- ResponseGastrointestinal EndoscopyVol. 77Issue 1
- PreviewWe thank Dr Shao and colleagues for their comments on our study.1 First, we agree that the association between the baseline characteristics and patient outcomes may cause the chance bias on a statistical test of outcome,2 and covariate adaptive allocation may reduce the imbalance of baseline covariates.3 In this study, we used blocked randomization (restricted randomization), and imbalance of baseline patient ages between the self-expandable metal stent (SEMS) group and the plastic stent (PS) group had occurred.
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