The Role of 68Ga-FAPI PET/CT in Breast Cancer Response Assessment and Follow-Up.

PURPOSE: 68Ga-fibroblast activation protein inhibitor (FAPI), a new PET/CT radiotracer targeting cancer-associated fibroblasts in tumor microenvironment, can detect many types of cancer. We aimed to assess whether it can also be used for response assessment and follow-up.

METHODS: We followed up patients with FAPI-avid invasive lobular breast cancer (ILC) before and after treatment changes and correlated qualitative maximal intensity projection images and quantitative tumor volume with CT results and blood tumor biomarkers.

RESULTS: Six consenting ILC breast cancer patients (53 ± 8 years old) underwent a total of 24 scans (baseline for each patient and 2-4 follow-up scans). We found a strong correlation between 68Ga-FAPI tumor volume and blood biomarkers (r = 0.7, P < 0.01), but weak correlation between CT and 68Ga-FAPI maximal intensity projection-based qualitative response assessment.

CONCLUSIONS: We found a strong correlation between ILC progression and regression (as assessed by blood biomarkers) and 68Ga-FAPI tumor volume. 68Ga-FAPI PET/CT could possibly be used for disease response assessment and follow-up.