A Phase 2 clinical trial at the University of Texas MD Anderson Cancer Center has revealed that delivering radiotherapy prior to surgical removal in estrogen receptor-positive breast cancer patients induces significant genomic and immune microenvironment changes. Single-cell RNA sequencing of tumors from 11 patients showed increases in macrophages, B cells, and CD4 T cells, alongside modulation of stress response and interferon-related genes within tumor cells. This pure assessment of radiation effects without preceding surgery could guide optimization of radiotherapy timing and combination therapies in breast cancer treatment, according to the study published in Cell Reports. Independent experts highlight the value of this direct examination of radiation’s biological impact.