A study by Kumar et al. in preclinical models of PR-positive breast cancer xenografts, with and without ESR1 mutations, demonstrated that [18F]FFNP could effectively detect a decrease in tracer uptake in wild-type tumors after 7 days of endocrine therapy, while no decrease was observed in ESR1-mutant tumors, indicating therapy resistance [120]. This evidence concerns the gene ESR1 and breast carcinoma.