Pharmacokinetics, biodistribution, and radiation dosimetry for ⁸⁹ Zr-trastuzumab in patients with esophagogastric cancer

Trastuzumab with chemotherapy improves clinical outcomes in patients with human epidermal growth factor receptor 2 (HER2)–positive esophagogastric adenocarcinoma (EGA). Despite the therapeutic benefit, responses are rarely complete, and most patients develop progression. To our knowledge, this is the first report evaluating ⁸⁹ Zr-trastuzumab in HER2-positive EGA; here, we evaluate the safety, pharmacokinetics, biodistribution, and dosimetry ⁸⁹ Zr-trastuzumab. Methods: Trastuzumab was conjugated with deferoxamine and radiolabeled with ⁸⁹ Zr. A mean activity of 184 MBq was administered to 10 patients with metastatic HER2-posi-tive EGA. PET imaging, whole-body probe counts, and blood draws were performed to assess pharmacokinetics, biodistribution, and dosimetry. Results: No clinically significant toxicities were observed. At the end of infusion, the estimated ⁸⁹ Zr-trastuzumab in plasma volume was a median 102% (range, 78%–113%) of the injected dose. The median biologic half-life T _1/2b was 111 h (range, 78–193 h). The median biologic whole-body retention half-life was 370 h (range, 257–578 h). PET images showed optimal tumor visualization at 5–8 d after injection. The maximum tumor SUV ranged from no to minimal uptake in 3 patients to a median of 6.8 (range, 2.9–22.7) for 20 lesions in 7 patients. Dosimetry estimates from OLINDA showed that the organs receiving the highest absorbed doses were the liver and heart wall, with median values of 1.37 and 1.12 mGy/MBq, respectively. Conclusion: ⁸⁹ Zr-trastuzumab imaging tracer is safe and provides high-quality images in patients with HER2-positive EGA, with an optimal imaging time of 5–8 d after injection.