CASE REPORT OF METASTATIC MELANOMA LESION AFFECTING AN EXTENSIVE AREA OF THE LEFT LOWER LIMB ON 18F-PSMA PET/CT AND 18F-FDG PET/CT IMAGES – INTENDING TO COMPARE THE DISTRIBUTION OF BOTH RADIOTRACERS IN THIS CANCER

Abstract

Introduction/Justification

Positron emission tomography (PET/CT) using 18F-FDG has been widely used for staging and monitoring melanoma patients. Recent studies highlight the potential of 18F-PSMA PET/CT as an additional diagnostic modality, given the expression of prostate-specific membrane antigen (PSMA) in melanoma cells. Recent evidence indicates that anti-PSMA antibodies react with malignant melanoma neo vasculature, coupled with incidental findings reporting PSMA avidity in melanoma, the potential role of 18F-PSMA PET/CT as a novel diagnostic imaging technique in non-prostatic cancers looks promising.

Report

We describe below a case that illustrates the potential of 18F-PSMA PET/CT in evaluate melanoma lesions: 72-year-old female patient, Caucasian, single, with medical history of chronic obstructive pulmonary disease, diabetes mellitus, hypertension, smoking for 10 years (50 pack-years), and a cerebral aneurysm clipping in 2013 (which resulting in inability to walk). In 2022, she developed a sudden and progressive lesion on her left hallux, which spread to left lower limb over six months. She underwent two biopsies, confirming the diagnosis of melanoma. In 2024, the subject presented on physical examination a lesion affecting all the posterior portion of the lower limb, associated to an ulcerated vegetative lesion of approximately 10 cm on the medial portion of the left hallux. The immunohistochemistry findings described an invasive and ulcerated melanoma (Breslow 5 mm). On 16-October-2024 she underwent a 18F-FDG PET/CT founding an extensive densification of the subcutaneous tissue throughout the entire left lower limb, associated with multiple nodules, measuring up to 6.8 × 3.2 cm (SUVmax = 36.9). Furthermore, it was found left inguinal and femoral lymphadenopathy, and multiple pulmonary and hepatic nodules (SUVmax = 30.3). On the following day (17-October-2024), it was performed a 18F-PSMA PET/CT which found uptake of the radiotracer on the primary lesion in the left lower limb (SUBmax = 22.7), in the regional lymph nodes (inguinal and femoral) and pulmonary nodules (SUVmax = 32.1). Comparatively, the 18F-PSMA radiotracer showed smoothly less intense uptake in the left lower limb lesion and pulmonary nodules compared to 18F-FDG. On the other hand, hepatic nodules did not present 18F-PSMA uptake, while 18F-FDG uptake was moderately intense (SUVmax = 9.7). Due to the patient's multiple comorbidities, advanced age, poor general condition (Karnofsky Performance Status of 40%), and high surgical risk, invasive treatment was contraindicated. Palliative care was chosen instead.

Conclusion

Therefore, apart from the use of 18F-PSMA PET/CT in staging of prostate cancer patients, this method shows a great potential in the evaluating of metastatic melanoma, with a capacity of uptake in lesions comparable to 18F-FDG PET/CT (as demonstrated in this case), needing further and longer studies to confirm these advantages.