A pictorial view on false positive findings of 68Ga-PSMA-11 PET/CT and their prognostic value in patients with prostate carcinoma after radical prostatectomy and undetectable PSA values.

OBJECTIVE: Recently, gallium-68-prostate-specific membrane antigen-11 (68Ga-PSMA-11) positron emission tomography/computed tomography (PET/CT) has become a key imaging method in prostate carcinoma staging and biochemical progression, with varying sensitivities in different studies (from 40% to 80%). After four years of experience with 68Ga-PSMA-11 PET/CT, we found that it is possible to detect lesions with increased PSMA expression in patients with undetectable prostate specific antigen (PSA) levels after radical prostatectomy. The key questions we wanted to answer were as follows: if those lesions were malignant and could the early detection of those malignant lesions have a role in patient management? We aimed to identify and follow up PSMA-positive findings for a period of 4 years in patients with prostate cancer after radical prostatectomy and undetectable PSA values at the time of the examination. We also explored false-positive lesions in detail. SUBJECTS AND METHODS: The study included all patients who underwent radical prostatectomy and had undetectable PSA values <0.05ng/mL and who underwent 68Ga-PSMA-11 PET/CT between July 2019 and December 2019. We performed 220 studies and found 40 patients with these characteristics; these patients were included in this study. All of them were followed up until July 2023. Any finding with increased radiopharmaceutical accumulation above the background activity in the respective area was considered a false positive. Prostate-specific membrane antigen accumulation in established lesions was assessed semi-quantitatively by the maximum standardized uptake value (SUVmax) and qualitatively by the four-point visual scale proposed in the E-PSMA recommendations. RESULTS: We found 15/40 (37.5%) patients with PSMA-positive findings. These were predominantly bone changes without a corresponding CT abnormality or discrete cystic or osteoblastic lesions with above-background increased PSMA expression. The mean SUVmax of these non-specific lesions was 3.02 (SD 2.86). After 3.5-4 years of follow-up, biochemical progression was found in only two of the patients.The great sensitivity of the method nowadays is a powerful engine for the development of new therapeutic options. On the other side, the lower specificity due to false positive findings, if misinterpreted, might lead to switching to a higher stage, with the planned radical treatment replaced by palliative treatment. CONCLUSION: The presence of 68Ga-PSMA-11 PET/CT-positive findings in patients after radical prostatectomy and an undetectable PSA had a low predictive value for future progression. The interpretation of 68Ga-PSMA-11 PET/CT should always include a complex assessment of the clinical setting-the risk group, PSA value and degree of PSMA accumulation in the lesions. In these situations, further clarification of PSMA-positive findings is appropriate before deciding to change treatment.

Diagnostic and clinical value of [18F]FDG PET/CT in the follow-up regimen in IIA-IIID stage cutaneous malignant melanoma after first regional recurrence.

BACKGROUND: Malignant melanoma stands out as a disease with highly aggressive behavior and frequent recurrences. It is crucial to find a non-invasive method for early recurrence detection which allows early and radical treatment. Our aim was to assess the diagnostic and clinical value of [18F]FDG PET/CT in the follow-up regimen of patients after radically treated first regional recurrence and for early detection of operable disease progression. MATERIAL AND METHODS: We performed [18F]FDG PET/CT in 96 consecutive patients who had a histologically proven regional recurrent disease that was radically treated. In 46 patients [18F]FDG PET/CT was used in the follow-up regimen and in the other 50 it was used for clarification of suspicious lesions seen in conventional studies. We explored the diagnostic performance of [18F]FDG PET/CT. We also compared the results with conventional studies and explored the clinical impact of [18F]FDG PET/CT by its ability to find localized disease progression in those groups. RESULTS: [18F]FDG PET/CT had better sensitivity, specificity, PPV and NPV, and accuracy in patients with symptoms. This good results in the second group had a high price for the patients, as there was a prevalence of distant metastatic disease in the second group - 64.0% vs. 28.3% in the surveillance group (p = 0.001). [18F]FDG PET/CT revealed more of the distant and in-transit lesions and assisted in lymph node detection by guiding the ultrasonography. Owing to the [18F]FDG PET/CT surveillance, 64.5% of all operable lesions were found in the surveillance group vs. only 35.5% in the second group, where the distant metastatic disease was prevalent. CONCLUSIONS: [18F]FDG PET/CT used as a follow-up tool in the surveillance regimen of patients after the first recurrence showed excellent performance in timely and accurate recognition of operable lesions. It had significantly better performance than conventional studies in the follow-up regimen of the patients in this high risk of progression group.