The Growth Modulation Index (GMI) as an Efficacy Outcome in Cancer Clinical Trials: A Scoping Review with Suggested...

The growth modulation index (GMI) is defined as the ratio between the time to progression of a new line of treatment and the previous line. This ratio can be used to determine whether the new line of treatment brings a clinical benefit. It has been proposed as an outcome in trials evaluating non-cytotoxic drugs. Its interest lies in the intra-patient comparison. The terminology employed to refer to the GMI, as well as its definitions, are highly variable in the literature. Some uses of the GMI are arbitrary and not based on any scientific rationale. Our aim is to describe how the GMI is reported in the scientific literature.

We carried out a scoping review using PubMed, Scopus, Web of Science and BASE (Bielefeld Academic Search Engine). The algorithm was composed of the terms "growth modulation index", "time to progression ratio" and "progression-free survival ratio". Documents in English, with full-text available, published up to 2023, were included. Among 227 included documents, 166 of which discussed GMI specifically. On these 166 documents, 76 reported on observational studies, 62 on interventional studies and 17 on methodological or statistical developments pertaining to the GMI. All were about oncology. Our review highlights significant variability in the reporting and use of the GMI. To address this, we propose standardized reporting guidelines. Additionally, we emphasize the need for methodological and statistical developments to improve the use of the GMI and to develop novel GMI-based trial designs.