FAP and breast cancer: Future studies in larger cohorts are warranted to explore the potential of FAP-targeted theranostics in different breast cancer subtypes.<h4>Trial registration</h4>68-Ga-FAPI-PET for Tumor Detection: A Prospective Observational Trial, NCT04571086, 09-15-2020, https://clinicaltrials.gov/study/NCT04571086 .