Abstract P3-03-22: Use of 64Cu-DOTA trastuzumab positron emission tomography to predict pathologic complete response in locally advanced HER2 positive breast cancer

Use of 64Cu-DOTA trastuzumab Positron Emission Tomography to predict pathologic complete response in locally advanced HER2 positive breast cancer. Background: We have demonstrated that 64Cu-DOTA trastuzumab is an effective PET imaging agent of HER2 positive breast cancer and correlated with HER2 status by IHC. Methods: Patients with locally advanced breast cancer were eligible if they had biopsy confirmed HER2 + disease, locally advanced disease and were to be treated with neoadjuvant therapy. Pretreatment staging included a breast MRI, 18F-FDG-PET/CT and 64Cu-trastuzumab-PET/CT (64CuT-PET). Prior to injection of 64Cu-trastuzumab, patients received 50 mg of cold trastuzumab per our previously established protocol. 64CuT-PET was obtained at 21-25 h over fields of view chosen in reference to MRI. Uptake in lesions was measured in terms of body wt-normalized SUV. Lesions with intensity > adjacent tissue were considered positive on PET. Breast MRI was obtained after 4 cycles of chemotherapy and preoperatively. Response to therapy was determined on the surgical specimen. Results: Eighteen women have completed study and are evaluable for treatment response. The median age was 56 years (Range 32-62); 5 were ER- and PR-; 13 ER+/- PR+. One patient had increased 64CuT-PET uptake at T4 which was not appreciated on conventional imaging and subsequent biopsy confirmed metastatic disease. She is included in the analysis as she ultimately underwent surgical management of the breast. Complete pathologic response was seen in 14/18 patients - 11/14 ER+/- PR + and 3/4 ER-/PR-. Four patient had residual disease at surgery; 3 of 4 were HER2 negative and 1 was HER2+. Uptake on 64CuT-PET correlated with increased uptake on 18F-FDG-PET. The ratio of 64CuT-PET: 18F-FDG-PET ≥ 0.7 was associated with complete pathologic response at surgery.Conclusions: The ratio of 64CuT-PET to 18F-FDG-PET ≥ 0.7 was associated with complete pathologic response in women undergoing neoadjuvant chemotherapy for locally advanced HER2+ breast cancer. Residual disease after HER2-directed therapy was frequently HER2 negative. Citation Format: Joanne Mortimer, Russell Rockne, Jessica Liu, Yuan Yuan, Daphne Stewart, James Waisman, Paul Frankel, Laura Kruper, Vikram Adhikarla. Use of 64Cu-DOTA trastuzumab positron emission tomography to predict pathologic complete response in locally advanced HER2 positive breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-03-22.