Use of 64Cu-DOTA-Trastuzumab PET to Predict Response and Outcome of Patients Receiving Trastuzumab Emtansine (T-DM1) for Metastatic Breast Cancer: A Pilot Study.

Trastuzumab emtansine (T-DM1) is an antibody drug conjugate used to treat HER2-positive breast cancer. We hypothesized that functional imaging with 64Cu-DOTA-trastuzumab PET/CT would predict patient response to T-DM1 therapy. Methods: Ten women with biopsy-proven HER2-positive metastatic breast cancer who were to be treated with T-DM1 underwent pretreatment 18F-FDG PET/CT. 64Cu-DOTA-trastuzumab PET/CT was performed 1 and 2 days post-injection. Treatment outcome was assessed by (a) response to T-DM1 (3.6 mg/kg every 3 wk) as evaluated by follow-up 18F-FDG PET/CT using PERCIST criteria and (b) time to treatment failure (TTF). Tumors measurable for response were evaluated for 64Cu-DOTA-trastuzumab uptake in terms of maximum voxel standardized uptake value (SUVmax, units g/mL). Results: Response was clearly related to tumor uptake of 64Cu-DOTA-trastuzumab. Comparing group means, responsive patients (n = 5) had higher day 1 minimum SUVmax (5.6 vs 2.8, P threshold (P < 0.01). Patients with day 2 minimum SUVmax above versus below threshold had median TTF = 28 months versus 2 months (P < 0.02).