Abstract
We hypothesized that functional imaging with (64)Cu-DOTA-trastuzumab PET/CT would predict the response to the antibody-drug conjugate trastuzumab-emtansine (T-DM1). Methods: Ten women with metastatic human epidermal growth factor receptor 2-positive breast cancer underwent (18)F-FDG PET/CT and (64)Cu-DOTA-trastuzumab PET/CT on days 1 and 2 before treatment with T-DM1. Results: T-DM1-responsive patients had higher uptake than nonresponsive patients. Day 1 minimum SUV(max) (5.6 vs. 2.8, P < 0.02), day 2 minimum SUV(max) (8.1 vs. 3.2, P < 0.01), and day 2 average SUV(max) (8.5 vs. 5.4, P < 0.05) for (64)Cu-DOTA-trastuzumab all favored responding patients. Tumor-level response suggested threshold dependence on SUV(max) Patients with a day 2 minimum SUV(max) above versus below the threshold had a median time to treatment failure of 28 mo versus 2 mo (P < 0.02). Conclusion: Measurement of trastuzumab uptake in tumors via PET/CT is promising for identifying patients with metastatic breast cancer who will benefit from T-DM1.