Randomized controlled trials in relapsed/refractory follicular lymphoma: a systematic review and meta-analysis

This systematic literature review evaluated the clinical efficacy and safety of interventions used in relapsed/refractory follicular lymphoma. Primary efficacy outcomes were objective response rate, progression-free survival and overall survival. Safety endpoints were grade 3/4 toxicities, serious adverse events and withdrawals or deaths due to toxicity. Studies were selected if they were randomized controlled trials reporting on the efficacy or safety of treatments for relapsed or refractory follicular lymphoma, and if outcomes were reported separately from trials that included other lymphoid neoplasms. We used the Bucher method for conducting adjusted indirect comparisons within a meta-analysis. We identified 10 randomized controlled trials of treatments for relapsed/refractory follicular lymphoma. The most prominent drug investigated (alone or in combination) was rituximab. Most trials did not report median overall survival. Two trials reported median event-free survival (range, 1.2-23.2 months). Six of ten trials reported objective response rate (range, 9-93%). Meta-analysis showed only one statistically significant result: rituximab + bortezomib yielded a significantly higher objective response rate than rituximab monotherapy (relative risk, 1.28; 95% confidence interval, 1.11-1.47). Otherwise, there were no discernable differences in overall survival or progression-free survival, partly due to insufficient reporting of results in the clinical trials. The relatively small number of randomized controlled trials, few overlapping treatment arms, and variability in the randomized controlled trial features and in the endpoints studied complicate the formal comparison of therapies for relapsed/refractory follicular lymphoma. Additional well-designed randomized controlled trials are needed to fully understand the relative outcomes of older and more recently developed therapies.