Application of sample stabilization and mass cytometry in global oncology trials: lessons from regulatory T cell monitoring

INTRODUCTION: Approximately 1.2 million flow cytometry specimens are processed annually in clinical trials. Sponsors analyze rare populations such as regulatory T cells (Tregs) to show whether a pharmacodynamic effect occurred. Two barriers limit this in global oncology trials: specimen degradation and slow panel development. METHODS: This review draws on three sources: published whole-blood cell-loss data; fresh-versus-fixed comparisons from the authors' laboratory; and serial Treg measurements from the first-in-human dose study of roginolisib. RESULTS: Across these sources, up to 20% of trial samples are excluded for exceeding transit windows. Fixation at draw preserves major immune population frequencies over 72 hours. In roginolisib, serial mass cytometry showed progressive Treg reductions linked to disease control and survival in metastatic uveal melanoma. CONCLUSION: Site-level fixation with mass cytometry removes the 72-hour shipping constraint. In the authors' experience, discrete mass-channel assignment also shortens qualification of a 20-marker panel from approximately 6 months to approximately 3 weeks, supporting Treg pharmacodynamic monitoring across global oncology trials.