Liver metastasis of a neuroendocrine tumor demonstrates intense uptake in PSMA-PET—but not its lymph-node metastasis and primary-tumor

During the last decade, PSMA-PET/CT became a mainstay in the imaging of prostate cancer. However, PSMA is also expressed in the neo-vasculature of various non-prostatic tumors [1]. Amongst other somatostatin receptor-targeted tracers, DOTATOC-PET/CT is the current gold standard for imaging of well-differentiated neuroendocrine tumors arising in the gastrointestinal tract [2]. This image presents a patient who was originally diagnosed with a high-grade prostate carcinoma (Gleason score 9, initial PSA 48 ng/ml). Consequently, an atypically located liver lesion was histologically proven to be a well-differentiated neuroendocrine tumor (G2). Due to his transplant kidney, the patient was not allowed to receive contrast media; hence, he received staging with [18F]F-PSMA-1007 and [68 Ga]Ga-DOTATOC PET/CT. In the PSMA-PET, the uptake of the prostate carcinoma was SUVmax 55.5 and the suspected liver metastasis was SUVmax 106.2; no uptake was seen in the neuroendocrine primary tumor and only faint uptake (SUVmax 8.5) in a peritoneal lymph node. In the DOTATOC-PET, the uptake of the duodenal neuroendocrine primary tumor was SUVmax 67.9, the positive lymph node in the related drainage was SUVmax 91.2, and the liver metastasis was SUVmax 221.3; the adenocarcinoma of the prostate was somatostatinreceptor negative. The presented image contains two interesting points. First, it demonstrates the high variability of PSMA expression in non-prostatic tumor lesions and its dependency of the local tumor microenvironment (e.g., site of metastasis, neoangiogenetic activity, organ-specific perfusion effects). Second, it serves as a reminder that an uncritical belief in strong biological signals obtained with highly specific


Image of the month
During the last decade, PSMA-PET/CT became a mainstay in the imaging of prostate cancer. However, PSMA is also expressed in the neo-vasculature of various non-prostatic tumors [1]. Amongst other somatostatin receptor-targeted tracers, DOTATOC-PET/CT is the current gold standard for imaging of well-differentiated neuroendocrine tumors arising in the gastrointestinal tract [2].
This image presents a patient who was originally diagnosed with a high-grade prostate carcinoma (Gleason score 9, initial PSA 48 ng/ml). Consequently, an atypically located liver lesion was histologically proven to be a well-differentiated neuroendocrine tumor (G2). Due to his transplant kidney, the patient was not allowed to receive contrast media; hence, he received staging with [ 18 F]F-PSMA-1007 and [ 68 Ga]Ga-DOTATOC PET/CT.
In the PSMA-PET, the uptake of the prostate carcinoma was SUV max 55.5 and the suspected liver metastasis was SUV max 106.2; no uptake was seen in the neuroendocrine primary tumor and only faint uptake (SUV max 8.5) in a peritoneal lymph node. In the DOTATOC-PET, the uptake of the duodenal neuroendocrine primary tumor was SUV max 67.9, the positive lymph node in the related drainage was SUV max 91.2, and the liver metastasis was SUV max 221.3; the adenocarcinoma of the prostate was somatostatinreceptor negative.
The presented image contains two interesting points. First, it demonstrates the high variability of PSMA expression in non-prostatic tumor lesions and its dependency of the local tumor microenvironment (e.g., site of metastasis, neoangiogenetic activity, organ-specific perfusion effects). Second, it serves as a reminder that an uncritical belief in strong biological signals obtained with highly specific This article is part of the Topical Collection on Image of the month.
tracers can lead to an overestimate of the "histo-radiological" performance of molecular imaging. A clinically uncommon situation-such as suspicion of liver metastatic prostate cancer without additional lymph node or bone metastases-still needs histopathological validation! Funding Open Access funding enabled and organized by Projekt DEAL.

Data Availability
The data that support the findings of this study are available from the corresponding author, EW, upon reasonable request.

Declarations
Competing interest The authors have no competing interests to declare that are relevant to the content of this article. This is a fully anonymized image obtained in clinical practice; no ethics approval is required for this kind of report.
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