Is it stage III melanoma and stage IV prostate cancer or stage IV melanoma bone and lymph node metastases? That's the question doctors recently faced when an elderly man with PSMA-expressing metastases presented to a German clinic. He was previously treated for prostate cancer and melanoma.

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Positron emission tomography (PET) with 68Ga prostate-specific membrane antigen (PSMA) and computed tomography (CT) can detect metastases in prostate cancer. However, PSMA expression can sometimes occur in other tumors as well, making it difficult to establish a clear diagnosis.

In 2019, a 70-year-old patient was diagnosed with melanoma of the left forearm (Breslow depth 1.4 mm, no lesion [pT2a]) after complete excision, local re-excision with a safety margin of 10 mm was performed. At the patient's request, a sentinel biopsy was not performed at this time.
He was diagnosed with prostate cancer 13 years ago and treated with radical prostatectomy and salvage radiotherapy for recurrence 5 years after diagnosis.
During a test in 2022, an elevated serum level of prostate-specific antigen (PSA) was detected (0.58ng/ml) and a PSMA-PET/CT was ordered to detect possible recurrence. It demonstrated two lesions: a PSMA-positive, significantly enlarged left axillary lymph node and a PSMA-positive osteolytic lesion in the L5 lumbar vertebral body.