Abstract P5-03-06: Clinical value of 89Zr-trastuzumab PET in HER2-positive breast cancer patients with a clinical dilemma

Abstract

Abstract Background: Information on human epidermal growth factor receptor 2 (HER2) is essential for management of metastatic breast cancer (mBC). In patients suspected of HER2-positive mBC, standard work up may fail to clarify whole body HER2 status. We aimed to assess whether 89Zr-trastuzumab PET can support treatment decisions in patients posing this clinical dilemma. Methods: 89Zr-trastuzumab PET was performed as described earlier (Gaykema et al, Clin Cancer Res 2014) in patients in whom standard work up with bone scan, FDG PET, CT and if feasible a biopsy, failed to evaluate HER2 status of their disease. 89Zr-trastuzumab PET was defined positive, when at least a dominant part of the tumor load showed substantial tracer uptake (Gebhart et al, Ann Oncol 2015), when tumor tracer uptake in single lesions (except brain) was ≥ normal liver uptake or when brain metastases had a tracer uptake > background. Circulating tumor cell (CTC) analysis prior to tracer injectionwas performed using the CellSearch System (Janssen Diagnostics LLC) and CTC HER2 status was assessed immunofluorescently. Questionnaires about treatment decisions were completed before, directly after and ≥3 months after 89Zr-trastuzumab PET. Results: Twenty patients were enrolled: 8 with two primary cancers (HER2-positive and HER2-negative BC or BC and non-BC), 7 with metastases inaccessible for biopsy, 4 with prior HER2-positive and HER2-negative metastases, 1 with primary BC with equivocal HER2 status (average 4.23 HER2 gene copies/nucleus). 89Zr-trastuzumab PET was positive in 12 patients, negative in 7 and equivocal in one patient. In 15/20 patients 89Zr-trastuzumab PET supported treatment decision. The scan altered treatment of 8 patients, increased physicians' confidence without affecting treatment in 10, and improved physicians' understanding of disease in 18 patients. Ten patients had 1-99 CTCs, 6 with HER2 expression. There was no correlation between HER2 expression by CTCs and 89Zr-trastuzumab PET results or subsequent treatment decision. Conclusion: 89Zr-trastuzumab PET, but not CTC analysis, supports clinical decision making in BC patients in whom standard work up fails to evaluate HER2 status. (Funded by the Dutch A Sister's Hope). Citation Format: Schröder CP, Bensch F, Brouwers AH, Lub-de Hooge MN, de Jong JR, van der Vegt B, Sleijfer S, de Vries EG. Clinical value of 89Zr-trastuzumab PET in HER2-positive breast cancer patients with a clinical dilemma [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-03-06.