The clinical utility of FES-PET with multiple malignancies: A case report of advanced melanoma and breast cancer

Differentiating the primary etiology of metastatic lesions in patients with multiple malignancies can create challenges when it is not feasible to perform a biopsy. We present a case of a 62-year-old patient with metastatic estrogen receptor (ER)+/progesterone receptor (PR)+/human epidermal growth factor 2 amplified breast cancer, metastatic melanoma, and chronic lymphocytic leukemia who developed new pulmonary nodules not amenable to biopsy. Classic fluorodeoxyglucose positron emission tomography (PET) computed tomography (CT) imaging revealed metabolically active pulmonary lesions, but was unable to distinguish which primary cancer was responsible for the metastatic lesion. Subsequent PET/CT using 16α-[18F]-fluoro-17β-estradiol ([18F]FES) radioactive tracer, which binds to estrogen receptors, revealed tracer uptake within the pulmonary nodules, supporting that the new nodules were of breast primary, rather than melanoma. This non-invasive imaging was able to provide diagnostic clarity and directly inform management, leading to a change in systemic therapy. This case highlights the value of FES-PET/CT in characterizing ER-positive disease and distinguishing between competing malignancies when tissue biopsy is not feasible.