Tag Archive for: retrospective studies

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Article of the Month: Immortal-Time Bias in Urological Research

Every Month the Editor-in-Chief selects an Article of the Month from the current issue of BJUI. The abstract is reproduced below and you can click on the button to read the full article, which is freely available to all readers for at least 30 days from the time of this post.

In addition to the article itself, there is an accompanying editorial written by a prominent member of the urological community. This blog is intended to provoke comment and discussion and we invite you to use the comment tools at the bottom of each post to join the conversation.

Finally, the third post under the Article of the Week heading on the homepage will consist of additional material or media. This week we feature a video discussing the paper.

If you only have time to read one article this week, it should be this one.

Estimating the effect of immortal-time bias in urological research: a case example of testosterone-replacement therapy

 

Christopher J.D. Wallis*Rek Saskin†‡, Steven A. Narod§, Calvin Law, Girish S. Kulkarni† **, Arun Seth†† and Robert K. Nam*

 

*Division of Urology, Sunnybrook Health Sciences Centre, Institute for Health Policy, Management and Evaluation, University of Toronto, Institute of Clinical Evaluative Sciences, Sunnybrook Health Sciences Centre, §Department of Public Health Sciences, University of Toronto, Division of General Surgery, Sunnybrook Health Sciences Centre, **Division of Urology, University Health Network, University of Toronto, and ††Department of Anatomic Pathology, Platform Biological Sciences, Sunnybrook Health Sciences Centre, Toronto, ON, Canada

 

Abstract

Objective

To quantify the effect of immortal-time bias in an observational study examining the effect of cumulative testosterone exposure on mortality.

Patients and Methods

We used a population-based matched cohort study of men aged ≥66 years, newly treated with testosterone-replacement therapy (TRT), and matched-controls from 2007 to 2012 in Ontario, Canada to quantify the effects of immortal-time bias. We used generalised estimating equations to determine the association between cumulative TRT exposure and mortality. Results produced by models using time-fixed and time-varying exposures were compared. Further, we undertook a systematic review of PubMed to identify studies addressing immortal-time bias or time-varying exposures in the urological literature and qualitatively summated these.

Results

Among 10 311 TRT-exposed men and 28 029 controls, the use of a time-varying exposure resulted in the attenuation of treatment effects compared with an analysis that did not account for immortal-time bias. While both analyses showed a decreased risk of death for patients in the highest tertile of TRT exposure, the effect was overestimated when using a time-fixed analysis (adjusted hazard ratio [aHR] 0.56, 95% confidence interval [CI]: 0.52–0.61) when compared to a time-varying analysis (aHR 0.67, 95% CI: 0.62–0.73). Of the 1 241 studies employing survival analysis identified in the literature, nine manuscripts met criteria for inclusion. Of these, five used a time-varying analytical method. Each of these was a large, population-based retrospective cohort study assessing potential harms of pharmacological agents.

Conclusions

Where exposures vary over time, a time-varying exposure is necessary to draw meaningful conclusions. Failure to use a time-varying analysis will result in overestimation of a beneficial effect. However, time-varying exposures are uncommonly utilised among manuscripts published in prominent urological journals.

Editorial: Immortal-Time Bias – A Crucial Yet Overlooked Confounder in Urological Research

The measurement of treatment effect through observational studies has become commonplace in the medical literature. These cohort studies provide valuable data on outcomes that can be difficult to assess in randomized controlled trials, such as long-term mortality. Accurate interpretation of observational data, however, requires accounting for potential confounders of study design, including the immortal-time bias. In this issue of BJUI, Wallis et al. [1] show how accounting for this bias can influence the measured effect of cumulative testosterone exposure on mortality. The implications of their findings extend to several other studies, whose designs may also be subject to immortal-time bias.

‘Immortal time’ refers to the portion of a follow-up period during which an outcome could not have occurred (e.g. subjects in the ‘exposure group’ cannot die before they receive the exposure); thus, potentially allowing the artificial magnification of an effect on the study outcome [2]. As the authors point out, this concept is not new. It was first identified several decades ago to highlight how a study’s finding of a survival advantage for patients undergoing heart transplant was nullified once immortal time was properly accounted for [3]. Despite its long existence in epidemiological teachings, the authors cite several studies both within and outside of the urological literature that have failed to appropriately account for this bias. Many of these studies employ binary exposure variables, but Wallis et al. delve into relatively uncharted territory by examining the effect of immortal-time bias on multi-level categorical exposures.

The relationship between testosterone replacement therapy (TRT) and mortality, the focus of the accompanying study, is apt because it is a controversial topic that weighs heavily on an accurate assessment of the therapy’s risks and benefits. The authors, using data from their own prior study, show that this delicate balance can be easily tipped when immortal-time bias is not properly accounted for. In their analysis, the overall result was the same regardless of controlling for this bias; men in the lowest tertile of TRT exposure had a higher risk of mortality, and those in the highest tertile had a lower risk of mortality; however, use of a time-fixed as opposed to the more appropriate time-varying analysis led to a substantial magnification of the effect size in each direction. While the overall result may have been the same in this example, the authors cite other instances of high-impact research whose published conclusions were shown to be completely different once accounting for immortal-time bias [4]. One can easily imagine how this type of erroneous data analysis could have deleterious consequences in the clinical setting. Healthcare providers rely on research to make decisions that have far-reaching impacts on patients’ lives. This study highlights the importance of ensuring that such analyses are carried out properly so that patients can receive the high-quality, evidence-based care they deserve.

The authors should be commended for taking the time to deconstruct and evaluate an analytical concept that is pertinent to study designs across several disciplines. Much of the research published today seeks to find answers to important clinical questions, but not nearly enough investigation is devoted to verifying that the analyses to obtain these answers are conducted properly. Urology in particular is a field that is still maturing with respect to the use of secondary data analytical techniques, such as propensity score models and instrumental variables [5]. To sustain our improvement in investigative skills alongside our fellow medical disciplines, we must pay special attention to studies that hold a magnifying glass to commonly used methodologies in the urological literature. In a similar vein, there have been increasing efforts recently to improve the process and transparency of corroborating the results of scientific studies, and these authors’ findings reinforce why these efforts are so crucial. If we expect to continue pushing forward the boundaries of medical research, it is our duty to ensure that our analytical methods are as rigorous and accurate as possible.

Sean A. Fletcher, Philipp Gild and Quoc-Dien Trinh
Division of Urological Surgery and Center for Surgery and Public Health, Harvard Medical School, Brigham and Womens Hospital, Boston, MA, USA

 

 

References

 

 

2 Suissa S. Immortal time bias in pharmaco-epidemiology. Am J Epidemiol 2008; 167: 4929

 

3 Gail MH. Does cardiac transplantation prolong life? A reassessment Ann Intern Med 1972; 76: 8157

 

4 van Walraven C, Davis D, Forster AJ et al. Time-dependent bias was common in survival analyses published in leading clinical journals. J Clin Epidemiol 2004; 57: 67282

 

5 Cole AP, Trinh QD. Secondary data analysis: techniques for comparing interventions and their limitations. Curr Opin Urol 2017; 27: 3549

 

Video: Immortal-Time Bias in Urological Research

Estimating the effect of immortal-time bias in urological research: a case example of testosterone-replacement therapy

 

Read the full article

Abstract

Objective

To quantify the effect of immortal-time bias in an observational study examining the effect of cumulative testosterone exposure on mortality.

Patients and Methods

We used a population-based matched cohort study of men aged ≥66 years, newly treated with testosterone-replacement therapy (TRT), and matched-controls from 2007 to 2012 in Ontario, Canada to quantify the effects of immortal-time bias. We used generalised estimating equations to determine the association between cumulative TRT exposure and mortality. Results produced by models using time-fixed and time-varying exposures were compared. Further, we undertook a systematic review of PubMed to identify studies addressing immortal-time bias or time-varying exposures in the urological literature and qualitatively summated these.

Results

Among 10 311 TRT-exposed men and 28 029 controls, the use of a time-varying exposure resulted in the attenuation of treatment effects compared with an analysis that did not account for immortal-time bias. While both analyses showed a decreased risk of death for patients in the highest tertile of TRT exposure, the effect was overestimated when using a time-fixed analysis (adjusted hazard ratio [aHR] 0.56, 95% confidence interval [CI]: 0.52–0.61) when compared to a time-varying analysis (aHR 0.67, 95% CI: 0.62–0.73). Of the 1 241 studies employing survival analysis identified in the literature, nine manuscripts met criteria for inclusion. Of these, five used a time-varying analytical method. Each of these was a large, population-based retrospective cohort study assessing potential harms of pharmacological agents.

Conclusions

Where exposures vary over time, a time-varying exposure is necessary to draw meaningful conclusions. Failure to use a time-varying analysis will result in overestimation of a beneficial effect. However, time-varying exposures are uncommonly utilised among manuscripts published in prominent urological journals.

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Article of the week: Out of the COLD: cryoablation for locally advanced PCa

Every week the Editor-in-Chief selects the Article of the Week from the current issue of BJUI. The abstract is reproduced below and you can click on the button to read the full article, which is freely available to all readers for at least 30 days from the time of this post.

In addition to the article itself, there is an accompanying editorial written by a prominent member of the urological community. This blog is intended to provoke comment and discussion and we invite you to use the comment tools at the bottom of each post to join the conversation.

If you only have time to read one article this week, it should be this one

Cryoablation for locally advanced clinical stage T3 prostate cancer: a report from the Cryo-On-Line Database (COLD) Registry

John F. Ward, Christopher J. DiBlasio*, Christopher Williams, Robert Given and J. Stephen Jones

§The University of Texas MD Anderson Cancer Center, Houston, TX, *Urology, Mount Sinai School of Medicine, Huntington, NY, Urology, University of Florida and Shands Medical Center, Jacksonville, FL, Urology, Eastern Virginia Medical School, Norfolk, VA, and §Urology, Cleveland Clinic Lerner College of Medicine, Cleveland, OH, USA

Read the full article
OBJECTIVE

• To assess the oncological and functional outcomes of primary prostate cryoablation for men with clinical stage T3 (cT3) prostate cancer, as although radical prostatectomy (RP) or external beam radiotherapy (EBRT) are the standard treatments for locally advanced cT3 prostate cancer some patients opt for nonextirpative prostate cryoablation instead.

PATIENTS AND METHODS

• The Cryo-On-Line Database (COLD) Registry was queried to identify patients with cT3 prostate cancer treated with whole-gland cryoablation (366 patients).

• We assessed biochemical disease-free survival (bDFS) using the Phoenix definition and determined reported rates of urinary incontinence and retention, sexual activity, and rectourethral fistulisation after treatment.

• Patients were subsequently assessed according to whether they were administered neoadjuvant androgen-deprivation therapy or not (ADT; 115 patients, 31.4%).

RESULTS

• For the entire cohort, the 36- and 60-month bDFS rates were 65.3% and 51.9%, respectively.

• Patients who received neoadjuvant ADT had statistically nonsignificantly higher 36- and 60-month bDFS rates (68.0% and 55.4%, respectively) than patients who did not receive neoadjuvant ADT (55.3% and 36.9%, respectively).

• The after treatment urinary incontinence rate was 2.6%; urinary retention rate, 6.0%; sexual activity rate, 30.4%; and rectourethral fistulisation rate, 1.1%.

CONCLUSIONS

• Cryoablation for patients with cT3 prostate cancer leads to less favourable bDFS than that after RP or RT for the same group of men.

• The after treatment rectourethral fistulisation rates for patients with cT3 disease are higher than in those with organ-confined prostate cancer treated with cryoablation; however, urinary dysfunction and sexual activity rates are similar for men with cT3 to those reported from this same registry in men with cT2 disease.

• The addition of neoadjuvant ADT (though not studied prospectively here) should be strongly considered if a patient with cT3 prostate cancer is to be treated with cryoablation.

 

Editorial: Cryosurgery for clinical T3 prostate cancer

There are limited data available on the outcomes of cryosurgery for clinical T3 prostate cancer, and as such, the role of cryosurgery for clinical T3 disease is currently undetermined [1]. Modern cryosurgery of the prostate, utilizing gas-based third-generation technology, a real-time monitoring system with ultrasonography and thermocouples, is associated with a low complication rate [7], although comparative outcomes of the different treatment modalities and long-term follow-up data remain to be seen.

Several aspects of cryosurgery can make it difficult to adequately control locally advanced prostate cancer. First, cryosurgery for clinical T3 cancer requires unique surgical expertise to control local disease while minimizing side-effects. Secondly, staging of locally advanced prostate cancer is challenging – it is difficult to accurately identify the extent of extracapsular extension, seminal vesicle involvement and/or lymph node metastasis. Thirdly, challenges in managing clinical T3 disease include the requirement of a more extensive ablation technique to appropriately target the extraprostatic disease and seminal vesicle involvement as well as treatment for possible microscopic metastasis, which might not be clinically detectable.

Two recent randomized trials compared outcomes of external beam radiation therapy with those of cryosurgery (including cT3 diseases with use of neo-adjuvant androgen deprivation therapy [ADT]), with contrasting results [2, 3]. Chin et al. [2] reported superiority of biochemical disease-free survival favouring external beam radiation therapy in relatively more advanced (bulky) disease, while Donnelly et al. [3] reported significantly fewer positive biopsy rates favouring cryosurgery in the relatively less advanced disease. These findings could suggest that more advanced bulky cases that require wider local control of bulky extraprostatic diseases are not suitable for cryosurgery, while in appropriately selected cases with fewer extraprostatic diseases, cryosurgery is an acceptable option (when combined with neo-adjuvant ADT). Although appropriately extended cryo-lesions that achieve lethal temperatures can control extraprostatic disease, there is a certain limitation in the extension of cryo-lesions without injury to vital peri-prostate organs, such as the urinary sphincter, rectal wall, bladder wall and ureters.

Evolving accuracy of preoperative diagnostic imaging to assess extraprostatic disease can enhance outcomes, and staging tissue sampling from suspected extraprostatic disease could also identify actual microscopic extension of the extraprostatic disease [4]. A recently updated nomogram predicting lymph node invasion [5] suggests that the probability of lymph node invasion in patients with cT3, PSA level >10 ng/mL, and biopsy primary Gleason grade 4 is 20% or greater. Clearly, the preoperative risk assessment of lymph node involvement using such a modern calculator is pertinent for appropriate patient selection. Finally, management decision should be made by a multidisciplinary team.

When combined with radiotherapy, neo-adjuvant ADT for high-risk and locally advanced prostate cancer has been associated with clinical benefit; however, when combining neo-adjuvant ADT with prostatectomy, there is pathological down-staging and reduction in the surgical positive margin but minimal improvement in overall or disease-free survival [6]. The role of neo-adjuvant and adjuvant ADT when combined with cryosurgery is still unknown. Clearly, a prospective study is needed to determine the optimal duration and method of ADT (whether to use LHRH analogue or combined blockade) and to analyse the side-effects, the quality of life and the cost-effectiveness of a combination of cryosurgery with ADT for cT3a and cT3b prostate cancer.

Osamu Ukimura, Andre Luis de Castro Abreu, Andrew J. Hung and Inderbir S. Gill
USC Institute of Urology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA

Read the full article

References

  1. Babaian RJ, Donnelly B, Bahn D et al. Best practice statement on cryosurgery for the treatment of localized prostate cancer. J Urol 2008; 180: 1993–2004
  2. Chin JL, Al-Zahrani AA, Autran-Gomez AM, Williams AK, Bauman G. Extended followup oncologic outcome of randomized trial between cryoablation and external beam therapy for locally advanced prostate cancer (T2c-T3b). J Urol 2012; 188: 1170–1175
  3. Donnelly BJ, Saliken JC, Brasher PM et al. A randomized trial of external beam radiotherapy versus cryoablation in patients with localized prostate cancer. Cancer 2010; 116: 323–330
  4. Ukimura O, Coleman JA, de la Taille A et al. Contemporary role of systematic prostate biopsies: indications, techniques, and implications for patient care. Eur Urol 2013; 63: 214–230
  5. Briganti A, Larcher A, Abdollah F et al. Updated nomogram predicting lymph node invasion in patients with prostate cancer undergoing extended pelvic lymph node dissection: the essential importance of percentage of positive cores. Eur Urol 2012; 61: 480–487
  6. Shelley MD, Kumar S, Wilt T, Staffurth J, Coles B, Mason MD. A systematic review and meta-analysis of randomised trials of neo-adjuvant hormone therapy for localised and locally advanced prostate carcinoma. Cancer Treat Rev 2009; 35: 9–17
  7. Ward JF, DiBlasio CJ, Williams C, Given R, Jones JS. Cryoablation for locally advanced clinical stage T3 prostate cancer: a report from the Cryo-On-Line Database (COLD) Registry. BJU Int 2014; 113: 714–718

 

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