Pertuzumab is an anti-HER2 antibody that has been demonstratedto substantially enhance the rates of invasive-disease–freesurvival in patients with HER2-positive early breast cancer when combinedwith chemotherapy and trastuzumab.150 Thebiophysical mathematical model utilizes quantitative data obtainedfrom MRI and PET scans to estimate tumor density, perfusion, and HER2+targeted antibody distribution for individual patients. The gene discussed is ERBB2; the disease is breast carcinoma.