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Abstract
Radioactive iodine (RAI) is often used post-operatively for treatment of differentiated thyroid cancer (DTC), but many patients develop RAI-refractory disease. Patients with RAI-refractory DTC may be asymptomatic and stable for long periods of time, so identifying tumors that are no longer likely to respond to RAI treatment and determining when to transition to systemic therapy are critical issues for optimal patient care. The purpose of this paper is to review and assess the end points used in studies of RAI-refractory DTC in relation to the issues facing clinicians in transitioning patients to systemic therapy. Our goals are to provide a framework to help evaluate whether study results are clinically meaningful in guiding treatment decisions and to make recommendations to better define these end points for RAI-refractory DTC.
Acknowledgements
The authors thank B Kearney, consultant to MedVal Scientific Information Services, LLC, for providing medical writing and editorial assistance. This manuscript was prepared according to the International Society for Medical Publication Professionals’ “Good Publication Practice for Communicating Company-Sponsored Medical Research: The GPP2 Guidelines”.
Financial & competing interests disclosure
W Sacks is on the Scientific Advisory Panel for Bayer/Onyx Pharmaceuticals and GD Braunstein is on the Scientific Advisory Panel for Bayer/Onyx Pharmaceuticals and is a consultant to Genzyme/Sanofi. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. Writing assistance was utilized in the production of this manuscript and was funded by Eisai, Inc.
Advances in the molecular understanding of differentiated thyroid cancer (DTC) have led to the development of innovative and promising targeted therapies. Therefore, identifying tumors that are no longer likely to respond to radioactive iodine (RAI) treatment and determining when to transition to systemic therapy are critical issues for optimal patient care.
Overall survival has historically been the preferred primary end point in clinical trials of solid tumors, but progression-free survival (PFS) is becoming widely used as a surrogate measure of overall survival. PFS requires shorter study times, smaller study populations and is not affected by therapies used after disease progression on the study agent.
PFS is limited, however, in that defining and assessing progression vary from study to study, making it difficult to make meaningful comparisons between studies and their results.
Two recent Phase III clinical trials of tyrosine kinase inhibitors for treatment of RAI-refractory DTC have been performed. Both used PFS as the primary end point, and in both trials treatment with the active drug significantly improved PFS compared with placebo. But the two trials defined RAI-refractory disease differently, had different inclusion criteria and defined response slightly differently. These factors make it difficult to make clinically meaningful comparisons between the two studies.
As PFS has increasingly become the standard to guide clinical decision-making in RAI-refractory DTC, it is imperative that consensus in defining and measuring disease progression be established across study protocols.
The patient’s perspective is important in determining clinically meaningful end points for clinical trials. For many patients, the effect of treatment on quality of life can be more important than maximizing length of survival. Clinical study design, as well as clinical practice, should take these priorities into consideration.