Tumour Burden Reporting in Phase III Clinical Trials of Metastatic Lung, Breast, and Colorectal Cancers: A Systematic Review

SIMPLE SUMMARY: The initial tumour burden is a strong and well-known prognostic factor in oncology. A systematic review was performed to examine if and how the initial tumour burden is reported in phase III clinical trials in the most frequent and deadly cancers. Seventy trials were selected, which mostly included biologic agents. The identification of low-burden metastatic disease was performed in 28.6% of studies; it was a stratification factor for randomisation in only 25.7% of studies. In two studies, a significant imbalance between arms in patients with low-burden disease was revealed. Our findings emphasise the need for the better assessment of tumour burden in clinical trials. ABSTRACT: Background: Randomised phase III clinical trials represent a methodological milestone to select effective drugs against metastatic cancers. In this context, and particularly in the efficacy assessment of biologic drugs, the initial metastatic tumour burden is a strong prognostic factor. Methods: A systematic literature review of randomised, phase III, first-line, clinical trials in metastatic breast, colorectal, and lung cancers, published from 2016 to 2021, was performed. Three groups of variables were collected: identity-, method- (including tumour burden assessment) and outcome-related. Results: Seventy trials were selected. A large portion of studies (41.4%) focused on the effects of biologic agents (signal inhibitors and immuno-therapies). A definition of low-burden disease based predominantly on the number of involved organs was reported in 28.6% of studies. No explicit reference to oligo-metastatic disease was found either in inclusion/exclusion criteria or in final descriptive data analyses. Disease extent, heterogeneously defined, was a stratification factor for randomisation in only 25.7% of studies. In two studies, a significant imbalance between arms in patients with low-burden disease was revealed. Conclusions: Attention to initial tumour burden in designing future clinical trials (including the harmonisation of definitions and the reporting of eventual oligo-metastatic disease, complete estimates of tumour volume, and its consideration as a stratification factor) should be increased.