68Ga-HER2 affibody PET/CT imaging as an option in patients whose HER2 status of any tumor in the body needs to be deciphered.

1045 Background: Anti-HER2 targeted agents are standard of care for HER2 positive patients with either early or advanced breast cancer. Determination of tumor HER2 status helps diagnosing and treating breast cancer. In any tumor which required this biological information, we used a novel 68 Ga-NOTA-MAL-MZHER2 ( 68 Ga-HER2) affibody PET/CT to differentiate HER2 status of each lesion in the patient body. Methods: 68 Ga-HER2 affibody PET/CT was performed in breast cancer patients if HER2 status of any lesions in the patient body remained to be determined. Results: Twenty-four patients were enrolled. 68 Ga-HER2 affibody PET/CT was requested by physicians due to the following reasons: 6 with multiple primary cancers (including patients who harbored two primary breast malignancies but with different HER2 status, and patients who had at least another non-breast primary other than HER2-positve breast cancer), 13 with metastases inaccessible for biopsy or repeated biopsy, 6 with inconsistent HER2 status between the primary and metastatic lesions, and 4 with different HER2-status within metastases (ICH ranging from 0-3+). Assessment report showed that the 68 Ga-HER2 affibody tumor uptake was considered positive in 16 patients, negative in 7 patients, and equivocal in one patient. In 11 lesions which was pathological-confirmed HER2-positivity, 100% of the tumors were also positive with this PET/CT. The heterogeneity of 68 Ga-HER2 affibody uptake was obvious, with a maximal 8.5-fold difference within one patient and a maximal 11-fold difference among patients. Conclusions: 68 Ga-HER2 affibody PET/CT imaging is a valuable tool if HER2 status of any tumor needs to determined. We are now evaluating the 68 Ga-HER2 affibody PET/CT imaging as a non-invasive approach to classify the molecular subtype of metastatic breast cancer, and its potential application in the dynamic surveillance of anti-HER2 therapies.