Purpose: Systemic androgen-signaling inhibition added to ongoing androgen-deprivation therapy (ADT) improved clinical outcomes in patients with nonmetastatic castrationresistant prostate cancer without detectable metastases by conventional imaging (nmCRPC). Prostate-specific membrane antigen ligand positron emission tomography (PSMA-PET) detects prostate cancer with superior sensitivity to conventional imaging, but its performance in nmCRPC remains largely unknown. We characterized cancer burden in high-risk patients with nmCRPC using PSMA-PET.Experimental Design: We retrospectively included 200 patients with nmCRPC, prostate-specific antigen (PSA) >2 ng/mL, and high risk for metastatic disease [PSA doubling time (PSADT) of 10 months and/or Gleason score of 8] from six high-volume PET centers. We centrally reviewed PSMA-PET detection rate for pelvic disease and distant metas-tases (M1). We further evaluated SPARTAN patients stratified by risk factors for PSMA-PET-detected M1 disease.Results: PSMA-PET was positive in 196 of 200 patients. Overall, 44% had pelvic diseases, including 24% with local prostate bed recurrence, and 55% had M1 disease despite negative conventional imaging. Interobserver agreement was very high (k: 0.81-0.91). PSA 5.5 ng/mL, locoregional nodal involvement determined by pathology (pN1), prior primary radiation, and prior salvage radiotherapy independently predicted M1 disease (all P < 0.05).Conclusions: PSMA-PET detected any disease in nearly all patients and M1 disease in 55% of patients previously diagnosed with nmCRPC, including subgroups with PSADT of 10 months and Gleason score of 8. The value of PSMA-PET imaging for treatment guidance should be tested in future studies.
Bone is the most common site of distant metastatic spread in prostate adenocarcinoma. Prostatespecific membrane antigen uptake has been described in both benign and malignant bone lesions, which can lead to false-positive findings on 68 Ga-prostate-specific membrane antigen-11 positron emission tomography (68 Ga-PSMA-11 PET). The purpose of this study was to evaluate the diagnostic accuracy of 68 Ga-PSMA-11 PET for osseous prostate cancer metastases and improve bone uptake interpretation using semi-quantitative metrics. METHODS. 56 prostate cancer patients (18 pre-prostatectomy, 38 biochemical recurrence) who underwent 68 Ga-PSMA-11 PET/MRI or PET/CT examinations with osseous PSMA-ligand uptake were included in the study. Medical records were reviewed retrospectively by boardcertified nuclear radiologists to determine true or false positivity based on a composite endpoint. For each avid osseous lesion, biological volume, size, PSMA-RADS rating, maximum standardized uptake value (SUVmax), and ratio of lesion SUVmax to liver, blood pool, and background bone SUVmax were measured. Differences between benign and malignant lesions were evaluated for statistical significance, and cutoff values for these parameters were determined to maximize diagnostic accuracy. RESULTS. Among 56 participants, 13 patients (22.8%) had false-positive osseous 68 Ga-PSMA-11 findings and 43 patients (76.8%) had true-positive osseous 68 Ga-PSMA-11 findings. Twentytwo patients (39%) had 1 osseous lesion, 18 (32%) had 2-4 lesions, and 16 (29%) had 5 or more lesions. Cutoff values resulting in statistically significant (p<0.005) differences between benign and malignant lesions were: PSMA-RADS ≥4, SUVmax ≥4.1, SUVmax ratio of lesion to blood by on November 1, 2020. For personal use only. jnm.snmjournals.org Downloaded from pool ≥2.11, to liver ≥0.55, and to bone ≥4.4. These measurements corresponded to lesion-based 68 Ga-PSMA-11 PET lesion detection rate for malignancy of 80%, 93%, 89%, 21%, 89%, and a specificity of 73%, 73%, 73%, 93%, 60%, respectively. CONCLUSION. PSMA-RADS rating, SUVmax, and SUVmax ratio of lesion to blood pool can help differentiate benign from malignant lesions on 68 Ga-PSMA-11 PET. SUVmax ratio to blood pool above 2.2 is a reasonable parameter to support image interpretation and presented superior lesion detection rate and specificity when compared to visual interpretation by PSMA RADS. These parameters hold clinical value by improving diagnostic accuracy for metastatic prostate cancer on 68 Ga-PSMA-11 PET/MRI and PET/CT.
We present a case of a 61-year-old man with history of prostate cancer and rising PSA levels referred for restaging. 68 Ga-PSMA-11 PET/CT identified 2 lung nodules with low and moderate PSMA uptake. Subsequent 18 F-FDG PET/CT showed high hypermetabolism in the nodule with low PSMA uptake, and low hypermetabolism in the nodule with moderate PSMA uptake. The isolated pulmonary findings and metabolic appearance is an atypical presentation of prostate cancer metastases and raised concern for a second primary malignancy. Fine-needle aspiration of the 18 F-FDG active lung nodule confirmed metastatic prostatic adenocarcinoma that subsequently responded to androgen deprivation therapy and abiraterone acetate.
We present the case of an 87-year-old man with a history of melanoma metastatic to the lungs found to have an FDG-negative liver lesion that was initially thought to be benign. Follow-up CT revealed growth of the liver lesion despite excellent response to nivolumab therapy of the pulmonary melanoma metastases. Biopsy of the lesion confirmed primary hepatocellular carcinoma. Follow-up 18F-FDG PET/CT showed minimal FDG uptake, slightly above liver background, and subsequent 68Ga-PSMA-11 PET/MR showed focal, intense uptake of radiotracer in a different region of the tumor. These imaging findings support intratumor metabolic heterogeneity with radiotracer uptake in different tumor locations.
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