Noninferiority Trials of Reduced Intensity Therapies: SCORAD trial of Radiotherapy for Spinal Metastases

No mets here just my PTX

A trial in JAMA this week by Hoskin et al (the SCORAD trial) compared two different intensities of radiotherapy for spinal metastases.  This is a special kind of noninferiority trial, which we wrote about last year in BMJ Open.  When you compare the same therapy at two intensities using a noninferiority trail, you are in perilous territory.  This is because if the therapy works on a dose response curve, it is almost certain, a priori, that the lower dose is actually inferior - if you consider inferior to represent any statistically significant difference disfavoring a therapy.  (We discuss this position, which goes against the CONSORT grain, here.)  You only need a big enough sample size.  This may be OK, so long as you have what we call in the BMJ Open paper, "a suitably conservative margin of noninferiority."  Most margins of noninferiority (delta) are far from this standard.

The results of the SCORAD trial were consistent with our analysis of 30+ other noninferiority trials of reduced intensity therapies, and the point estimate favored - you guessed it - the more intensive radiotherapy.  This is fine.  It is also fine that the 1-sided 95% confidence interval crossed the 11% prespecified margin of noninferiority (P=0.06).  That just means you can't declare noninferiority.  What is not fine, in my opinion, is that the authors suggest that we look at how little overlap there was, basically an insinuation that we should consider it noninferior anyway.  I crafted a succinct missive to point this out to the editors, but alas I'm too busy to submit it and don't feel like bothering, so I'll post it here for those who like to think about these issues.

To the editor:  Hoskin et al report results of a noninferiority trial comparing two intensities of radiotherapy (single fraction versus multi-fraction) for spinal cord compression from metastatic cancer (the SCORAD trial)¹.  In the most common type of noninferiority trial, investigators endeavor to show that a novel agent is not worse than an established one by more than a prespecified margin.  To maximize the chances of this, they generally choose the highest tolerable dose of the novel agent.  Similarly, guidelines admonish against underdosing the active control comparator as this will increase the chances of a false declaration of noninferiority of the novel agent^2,3.  In the SCORAD trial, the goal was to determine if a lower dose of radiotherapy was noninferior to a higher dose. Assuming radiotherapy is efficacious and operates on a dose response curve, the true difference between the two trial arms is likely to favor the higher intensity multi-fraction regimen.  Consequently, there is an increased risk of falsely declaring noninferiority of single fraction radiotherapy⁴.  Therefore, we agree with the authors’ concluding statement that “the extent to which the lower bound of the CI overlapped with the noninferiority margin should be considered when interpreting the clinical importance of this finding.”  The lower bound of a two-sized 95% confidence interval (the trial used a 1-sided 95% confidence interval) extends to 13.1% in favor of multi-fraction radiotherapy.  Because the outcome of the trial was ambulatory status, and there were no differences in serious adverse events, our interpretation is that single fraction radiotherapy should not be considered noninferior to a multi-fraction regimen, without qualifications.

1.            Hoskin PJ, Hopkins K, Misra V, et al. Effect of Single-Fraction vs Multifraction Radiotherapy on Ambulatory Status Among Patients With Spinal Canal Compression From Metastatic Cancer: The SCORAD Randomized Clinical Trial. JAMA. 2019;322(21):2084-2094.

2.            Piaggio G, Elbourne DR, Pocock SJ, Evans SW, Altman DG, f CG. Reporting of noninferiority and equivalence randomized trials: Extension of the consort 2010 statement. JAMA. 2012;308(24):2594-2604.

3.            Jones B, Jarvis P, Lewis JA, Ebbutt AF. Trials to assess equivalence: the importance of rigorous methods. BMJ. 1996;313(7048):36-39.

4.            Aberegg SK, Hersh AM, Samore MH. Do non-inferiority trials of reduced intensity therapies show reduced effects? A descriptive analysis. BMJ open. 2018;8(3):e019494-e019494.