RT Journal Article SR Electronic T1 Detection of HER2-Positive Metastases in Patients with HER2-Negative Primary Breast Cancer Using 89Zr-Trastuzumab PET/CT JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1523 OP 1528 DO 10.2967/jnumed.115.172031 VO 57 IS 10 A1 Gary A. Ulaner A1 David M. Hyman A1 Dara S. Ross A1 Adriana Corben A1 Sarat Chandarlapaty A1 Shari Goldfarb A1 Heather McArthur A1 Joseph P. Erinjeri A1 Stephen B. Solomon A1 Hartmuth Kolb A1 Serge K. Lyashchenko A1 Jason S. Lewis A1 Jorge A. Carrasquillo YR 2016 UL http://jnm.snmjournals.org/content/57/10/1523.abstract AB Our objective was to determine whether imaging with a human epidermal growth factor receptor 2 (HER2)–targeted PET tracer can detect HER2-positive metastases in patients with HER2-negative primary breast cancer. Methods: Patients with HER2-negative primary breast cancer and evidence of distant metastases were enrolled in an Institutional Review Board–approved prospective clinical trial. Archived pathologic samples from the patient’s primary breast cancer were retested to confirm HER2-negative disease. Patients with confirmed HER2-negative primary breast cancer underwent 89Zr-trastuzumab PET/CT to screen for 89Zr-trastuzumab metastases. Metastases avid for 89Zr-trastuzumab by PET/CT were biopsied and pathologically examined to define HER2 status. Patients with pathologically proven HER2-positive metastases subsequently received off-protocol HER2-targeted therapy to evaluate treatment response. Results: Nine patients were enrolled, all of whom had pathologic retesting that confirmed HER2-negative primary breast cancer. Five demonstrated suggestive foci on 89Zr-trastuzumab PET/CT. Of these 5 patients, 2 had biopsy-proven HER2-positive metastases and went on to benefit from HER2-targeted therapy. In the other 3 patients, biopsy showed no evidence of HER2-positive disease, and their foci on 89Zr-trastuzumab PET were considered false-positive. Conclusion: In this proof-of-concept study, we demonstrated that 89Zr-trastuzmab PET/CT detects unsuspected HER2-positive metastases in patients with HER2-negative primary breast cancer. Although these are only initial results in a small sample, they are a proof of the concept that HER2-targeted imaging can identify additional candidates for HER2-targeted therapy. More specific HER2-targeted agents will be needed for clinical use.