A targeted radiotherapy approach using a PD-L1-directed lutetium-177 antibody slowed tumor growth and extended survival in a mouse model of triple-negative breast cancer. Researchers administered [177Lu]Lu-atezolizumab at two doses and tracked biodistribution with SPECT to connect delivered radiation with response. In the model, tumor volumes shrank significantly versus saline controls, and median survival increased from 35 days in controls to 52 days at 9.25 MBq and 60 days at 18.5 MBq. The authors reported favorable early safety signals based on organ histology and body weight monitoring over the study window. The results add another preclinical data point for aligning radiolabeled immunotherapy to biologically available surface targets in aggressive breast cancer subtypes. Translation will hinge on whether PD-L1 expression, dosimetry, and tolerability replicate in humans—especially in combination settings with immunotherapy.