Visual Abstract
Abstract
Trastuzumab deruxtecan (T-DXd), a human epidermal growth factor receptor 2 (HER2)–targeted antibody–drug conjugate, demonstrated remarkable efficacy in previously treated patients with HER2-low metastatic breast cancer (mBC), marking a new therapeutic option for this patient population. Prior studies with HER2 PET using 89Zr-radiolabeled antibodies were limited by high rates of imaging false positives for HER2-positive malignancy. In this retrospective study, we investigate whether these false positives (HER2-negative on pathology) could be explained by HER2-low lesions. Methods: A retrospective study was conducted of mBC patients who previously enrolled in 2 prospective HER2 PET imaging trials: NCT02286843 using 89Zr-trastuzumab and 89Zr-pertuzumab and NCT04692831 using 89Zr-ss-pertuzumab. Patients were included if paired HER2 PET scan and biopsy were performed within a 2-mo period. Of 56 total patients, 23 patients met the inclusion criteria. Pathology results for biopsied lesions were collected, without repeat interpretation, and lesions were classified as HER2-positive, HER2-low, or HER2-0. SUVmax of biopsied lesions were compared between pathologic classifications to determine whether lesion uptake intensity could differentiate between HER2-positive and HER2-low lesions. Results: All prior false-positive lesions on HER2 PET scans from NCT02286843 were reclassified as HER2-low (instead of HER2-negative). In the 89Zr-trastuzumab cohort, 3 lesions were HER2-positive (33%) and 6 were HER2-low (67%); in the 89Zr-pertuzumab cohort, 2 were HER2-positive (29%) and 5 were HER2-low (71%). In the 89Zr-ss-pertuzumab cohort (NCT04692831), 7 patients underwent recent biopsies of 8 total lesions demonstrating 1 HER2-positive (12%), 5 HER2-low (62%), and 2 HER2-0 lesions (25%). HER2 PET SUVmax of biopsied lesions were compared between HER2-positive and HER2-low lesions for the combination of all 3 radiotracer cohorts. HER2-low lesions had a significantly higher SUVmax (median, 12.7; interquartile range, 8.05) than did HER2-positive lesions (median, 6.4; interquartile range, 1.98; P = 0.01). Conclusion: HER2 PET imaging with 89Zr-radiolabeled antibodies detects HER2-low lesions in addition to HER2-positive lesions in patients with mBC, suggesting its ability to visualize the entire spectrum of HER2 expression. All prior false positives on 89Zr-trastuzumab and 89Zr-pertuzumab PET scans were reclassified as HER2-low. Lesion SUVmax is not reliable in differentiating HER2-positive from HER2-low lesions; however, it may be useful in distinguishing lesions expressing HER2 from HER2-0 lesions.
Footnotes
Published online May 8, 2025.
- © 2025 by the Society of Nuclear Medicine and Molecular Imaging.
This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.
SNMMI members
Login to the site using your SNMMI member credentials
Individuals
Login as an individual user