Changes in LAC/PYR between baseline and very early response assessment in a responder and nonresponder. A, C, F, and H, Coronal T1-weighted 3D spoiled gradient echo (SPGR) images with LAC/PYR map overlaid on the breast tumor. B, D, G, and I, Coronal reformatted DCE images obtained 150 seconds after intravenous injection of a gadolinium-based contrast agent. A patient with HER2+ breast cancer was imaged at baseline (A and B) and for ultra-early response assessment (C and D) following standard-of-care treatment and showed a decrease in LAC/PYR of 41% (E), indicating nonresponse. At surgery, non-pCR with residual invasive cancer was identified. Another patient with TNBC was imaged at baseline (F and G) and for ultra-early response assessment (H and I) following treatment with chemotherapy and a PARP inhibitor and showed an increase in LAC/PYR of 157% (J), indicating response. At surgery, pCR without residual invasive breast cancer was found. HER2+, HER2/neu positive.