A study in Cancer & Metabolism reports that knockdown of the circadian rhythm gene PER2 promotes resistance to immune checkpoint inhibitors in gastric cancer cells. The mechanism described involves reprogramming the metabolism of myeloid-derived suppressor cells (MDSCs), which can blunt anti-tumor immune responses. By linking a core circadian regulator to checkpoint sensitivity, the research adds to emerging evidence that timekeeping biology can shape tumor-immune dynamics. It also points to metabolic control of suppressive immune populations as a lever that could be explored to overcome resistance. The study supports a more biomarker-oriented view of immunotherapy response, where tumor-intrinsic and microenvironmental features may jointly determine efficacy.