Use of <sup>64</sup>Cu-DOTA-Trastuzumab PET to Predict Response and Outcome of Patients Receiving Trastuzumab Emtansine for Metastatic Breast Cancer: A Pilot Study
Joanne Mortimer, James R. Bading, Paul Frankel, Mary Carroll, Yuan Yuan, Jinha Park, Lusine Tumyan, Nikita Gidwaney, Erasmus Poku, John E. Shively, David Colcher
Abstract
We hypothesized that functional imaging with <sup>64</sup>Cu-DOTA-trastuzumab PET/CT would predict the response to the antibody–drug conjugate trastuzumab–emtansine (T-DM1). <b>Methods:</b> Ten women with metastatic human epidermal growth factor receptor 2–positive breast cancer underwent <sup>18</sup>F-FDG PET/CT and <sup>64</sup>Cu-DOTA-trastuzumab PET/CT on days 1 and 2 before treatment with T-DM1. <b>Results:</b> T-DM1–responsive patients had higher uptake than nonresponsive patients. Day 1 minimum SUV<sub>max</sub> (5.6 vs. 2.8, <i>P</i> < 0.02), day 2 minimum SUV<sub>max</sub> (8.1 vs. 3.2, <i>P</i> < 0.01), and day 2 average SUV<sub>max</sub> (8.5 vs. 5.4, <i>P</i> < 0.05) for <sup>64</sup>Cu-DOTA-trastuzumab all favored responding patients. Tumor-level response suggested threshold dependence on SUV<sub>max</sub>. Patients with a day 2 minimum SUV<sub>max</sub> above versus below the threshold had a median time to treatment failure of 28 mo versus 2 mo (<i>P</i> < 0.02). <b>Conclusion:</b> Measurement of trastuzumab uptake in tumors via PET/CT is promising for identifying patients with metastatic breast cancer who will benefit from T-DM1.