Introduction: Cancer is an important cause of morbidity and mortality in kidney transplant recipients. Despite being established as a critically important outcome by patients, caregivers and health professionals, inconsistency in how cancer outcomes are defined and reported in trials of kidney transplant recipients may limit decision-making. The aim of this study was to assess the spectrum and consistency of cancer outcomes in trials involving kidney transplant recipients.
Methods: ClinicialTrials.gov was searched from inception to October 2019 to identify all randomized controlled trials (RCTs) in adult kidney transplants recipients which included cancer as a pre-defined outcome. We extracted the details of all primary and secondary cancer outcomes, including type, timepoint and definition of cancer (histology, grade and stage).
Results: Among the 71 RCTs included, there was a total of 87 cancer outcomes. The majority of trials (n = 61, 86%) included cancer as a secondary outcome only, with 8 trials (11%) including cancer as a primary outcome and 2 (3%) including cancer as part of a composite primary outcome measure. The most common descriptions of cancer in these outcome measures was "malignancy" without specific reference to diagnostic criteria, histology, grade or cancer stage (40, 46%) or "cancer" without specific clarification (8, 9%). Some trials included mention of specific cancer types, with post-transplant lymphoproliferative disorder (13, 15%), non-melanoma skin cancer (10, 11%) and skin cancer (in general) (5, 6%) being the most common, but these were not defined. A range of timepoints were used, with a single timepoint at the end of the primary trial being the most frequent (38, 44%); 13 studies included measurement at several timepoints during the trial (15%). A range of metrics for measuring cancer outcomes were used, including cancer incidence (53, 61%), proportion with cancer (9, 10%), and time-to-event (5, 6%). No measurement metric was specified in 18 (21%) cancer outcome measures.
Conclusion: Cancer is one of the most important outcomes for patients post-transplantation, but cancer outcomes are very poorly defined and highly variable in RCTs. A core outcome for cancer for all trials in kidney transplant recipients should be developed that is consistent and meaningful to patients and clinicians.