Incidental Detection of Metastatic Malignant Melanoma on 68Ga–Prostate-Specific Membrane Antigen PET/CT Imaging: Correlative Imaging With FDG PET/CT and Review of the Literature

A single-center retrospective review of metastatic prostate cancer on PSMA position emission tomography/computed tomography: Beyond lymph nodes and bones

BACKGROUND

Prostate-specific membrane antigen (PSMA) Positron emission tomography/computed tomography (PET/CT) has become a crucial imaging modality for the staging of patients with prostate cancer. The purpose of this study is to retrospectively determine the frequency, anatomical distribution, and clinical-pathologic correlates of extra-nodal and extra-osseous metastatic prostate cancer detected on PSMA PET/CT.

METHODS

All available 650 PSMA PET/CT performed in patients with biopsy-proved prostate cancer in our institution between September 2021 and December 2023 were reviewed for the presence of extra-nodal and extra-osseous metastatic disease (M1C disease). Thirty-four patients with M1C disease were identified.

RESULTS

The most frequent sites of visceral/soft tissue metastases were the lungs (58.8%), liver (23.5%) and adrenal glands (20.6%). 75% of patients with lung metastases detected on PSMA PET/CT had concurrent intrathoracic lymph node involvement. A higher frequency of patients with M1C disease (55.9%) had a high Gleason score. The median prostate-specific antigen (PSA) level at the time of the PSMA scan was 20.16 ng/mL. There was a statistically significant association between PSA level and osseous disease (p = 0.004), as well as PSA level and nodal disease (p = 0.008). While a large number of patients had concurrent osseous and nodal disease (82.4% and 79.4%, respectively), no visceral/soft tissue sites demonstrated a significant association with the presence of osseous or nodal involvement.

CONCLUSIONS

Given the increasing utilization of PSMA PET/CT, increased knowledge of the location and pattern of distribution of visceral/soft tissue metastatic sites is crucial not only for staging but also to better understand patterns of therapeutic response. We identified the lungs, liver and adrenal glands as the most common visceral/soft tissue metastatic sites from prostate cancer. We found that higher PSA levels at the time of PSMA PET/CT imaging were positively associated with concurrent osseous and nodal involvement.

The value of 68 Ga-PSMA-11 PET/CT in patients with prostate cancer and inconclusive standard imaging at primary staging

OBJECTIVE

The current standard imaging recommended for primary staging of intermediate- and high-risk prostate cancer (PCa) consists of bone scintigraphy (BS) and computed tomography (CT). Some patients will have equivocal lesions or divergent findings on BS and CT, leading to inconclusive disease staging. Our aim was to investigate the value of 68 Ga-PSMA-11 PET/CT in PCa with inconclusive disease stage based on standard imaging.

METHODS

We made a single-center study of patients with newly diagnosed PCa who underwent a 68 Ga-PSMA-11 PET/CT due to equivocal findings or discrepancies between BS and CT from 1 January 2017 to 31 December 2020. The value of 68 Ga-PSMA-11 PET/CT was evaluated for each location of equivocal findings (regional lymphnode, nonregional lymphnodes, bones and other metastases) and on a patient level.

RESULTS

Seventy-six patients were included in the study (62 patients with 72 equivocal lesions, 14 with discrepancy between BS and CT). Equivocal lesions were predominately in the bones (61%, 44/72), or in the regional lymph nodes (17%, 12/72). 68 Ga-PSMA-11 PET/CT provided a conclusive diagnosis in 90% (65/72) of the equivocal lesions. All patients with discrepancies between BS and CT had definite answers after 68 Ga-PSMA-11 PET/CT. 68 Ga-PSMA-11 PET/CT also uncovered 32 additional sites of metastasis in 25 patients not visible by standard imaging.

CONCLUSION

68 Ga-PSMA-11 PET/CT provides a definite disease stage in more than 90% of newly diagnosed patients with inconclusive standard imaging. Furthermore, it revealed additional sites of metastasis in 25 patients not detected by standard imaging.

Identification of distinct genomic features reveals frequent somatic AHNAK and PTEN mutations predominantly in primary malignant melanoma presenting in the ureter

BACKGROUND

Primary malignant melanoma of the ureter is extremely rare. Genetic variants to the increased risk of developing the disease have not yet been investigated.

METHODS

Tumour mutation profiling for primary malignant melanoma of the ureter was performed by whole-exome sequencing. Immunohistochemistry was performed to verify histopathological features and the variants of predisposing genes and driver mutation genes. Furthermore, we conducted a literature review and Surveillance, Epidemiology and End Result-based study by searching public databases.

RESULTS

We identified 38 somatic single nucleotide variants and 9 somatic insertions and deletions (INDELs) in tumour specimens. After filtering with the Cancer Gene Census database, seven predisposing genes and two driver mutation genes were identified. Moreover, the immunohistochemical profile showed that tumour cells were positive for Melan-A, melanoma gp100 human melanoma black 45 (HMB45), S100 beta and P53. The expression levels of two driver mutation genes (phosphatase and tensin homolog (PTEN) and desmoyokin (AHNAK) and five predisposing genes (AT-rich interaction domain 1B (ARID1B), catalase, eukaryotic translation initiation factor 4 gamma 3 (EIF4G3), ANK3 and collagen type I) were significantly downregulated in tumour tissues compared to paracancerous tissues. In the literature review and Surveillance, Epidemiology and End Results-based study, patients with primary malignant melanoma of the urinary tract had worse clinical outcomes than patients with primary urothelial carcinoma after 1:2 propensity score matching (P = 0.010). Additionally, Cox multivariate analysis for patients with primary malignant melanoma of the urinary tract indicated that distant metastasis (hazard ratio = 1.185; P = 0.044) was an independent predictor for overall survival, and tumour focality (hazard ratio = 0.602; P = 0.017) and non-surgery (hazard ratio = 0.434; P = 0.003) were independent factors for tumour progression.

CONCLUSIONS

Our study is the first to provide evidence that the distinct phenotypes of primary malignant melanoma of the ureter may be due to different genetic variations. The prognosis of primary malignant melanoma of the urinary tract was poorer than that of primary urothelial carcinoma of the urinary tract.

Incidental Metastatic Melanoma Identified on 18F-FDOPA PET/CT With Confirmation by Histology

A 47-year-old woman with a history of surgically treated abdominal paraganglioma and left thigh melanoma underwent an F-FDOPA PET/CT for suspected locoregional recurrence of paraganglioma. F-FDOPA PET/CT disconfirmed this recurrence but revealed 2 FDOPA-avid left inguinal lymph nodes, confirmed on a subsequent F-FDG PET/CT. Excision and pathology characterized these lymph nodes as melanoma metastases. F-FDOPA PET/CT is a widely used and valuable tool in the assessment of paraganglioma, both for staging and recurrence detection. Uptake of FDOPA has only rarely been documented in metastatic melanoma that could be a pitfall for detecting neuroendocrine tumors.

Incidental Detection of Malignant Melanoma Brain Recurrence on 68Ga-Prostate-Specific Membrane Antigen PET/CT

A 76-year-old man with a prior medical history of resected malignant melanoma of the skull underwent Ga-prostate-specific membrane antigen (PSMA) PET/CT due to rising tumor markers of a known prostate carcinoma. Unexpected high Ga-PSMA brain uptake was encountered around the surgical cavity in the skull with initially no specific structural changes on anatomical imaging. Successive CT and MRI eventually revealed local melanoma brain recurrence at this site. This interesting case demonstrates the diagnostic potential of Ga-PSMA PET/CT imaging for detection of malignant melanoma brain recurrence.

An overview on prostate-specific membrane antigen uptake in malignancies other than prostate cancer: A pictorial essay

Prostate-specific membrane antigen (PSMA) is a Type II transmembrane glycoprotein which is extremely overexpressed in prostate cancer epithelial cells. Recently, PSMA-targeted small molecule labeled with 68Ga and 99mTc allowed precise molecular imaging of prostate cancer and PSMA-targeted small molecule labeled with 177Lu leads to the development of radionuclide-targeted therapy of prostate cancer. Despite its name, it has been shown that PSMA has been expressed in several malignancies which can be due to significant neovascularization. Present pictorial assay reports the nonspecific tracer uptake in some malignancies during 68Ga-PSMA positron-emission tomography/computed tomography imaging and 99mTc-PSMA scintigraphy.

68Ga/64Cu PSMA Bio-Distribution in Prostate Cancer Patients: Potential Pitfalls for Different Tracers

BACKGROUND

68Ga-PSMA is a widely useful PET/CT tracer for prostate cancer imaging. Being a transmembrane protein acting as a glutamate carboxypeptidase enzyme, PSMA is highly expressed in prostate cancer cells. PSMA can also be labeled with 64Cu, offering a longer half-life and different resolution imaging. Several studies documented bio-distribution and pitfalls of 68Ga-PSMA as well as of 64Cu- PSMA. No data are reported on differences between these two variants of PSMA. Our aim was to evaluate physiological distribution of these two tracers and to analyze false positive cases.

METHODS

We examined tracer bio-distribution in prostate cancer patients with negative 68Ga-PSMA PET/CT (n=20) and negative 64Ga-PSMA PET/CT (n=10). A diagnostic pitfall for each tracer was documented.

RESULT

Bio-distribution of both tracers was similar, with some differences due to renal excretion of 68Ga- PSMA and biliary excretion of 64Cu-PSMA. 68Ga-PSMA uptake was observed in sarcoidosis while 64Cu- PSMA uptake was recorded in pneumonitis.

DISCUSSION

Both tracers may present similar bio-distribution in the human body, with similar uptake in exocrine glands and high intestinal uptake. Similarly to other tracers, false positive cases cannot be excluded in clinical practice.

CONCLUSION

The knowledge of difference in bio-distribution between two tracers may help in interpretation of PET data. Diagnostic pitfalls can be documented, due to the possibility of PSMA uptake in inflammation. Our results are preliminary to future studies comparing diagnostic accuracies of 68Ga-PSMA and 64Cu-PSMA.

Targeting 5α-reductase with 99mTc labeled dutasteride derivatives for prostate imaging

To assess the suitability of 99mTc labeled 5α-reductase (5α-Rds) inhibitors for non-invasive targeting of prostate cancer (PCa) using Male Sprague Dawely Rat (MSDR) model. In this work, dutasteride (Cpd-1) a 5α-Rds inhibitor was derivatized to its dithiocarbamate analogue (Cpd-2) for subsequent synthesis of 99mTc(CO)3-dutasteride dithiocarbamate (Cpd-3) using tricarbonyl technique. To determine the structure of Cpd-3, for the first time a reference Re(CO)3-dutasteride dithiocarbamate (Cpd-4) was synthesized and characterized with NMR, ESIMS, HPLC and elemental analysis. HPLC was used to establish the identity of Cpd-3 using Cpd-4 as a reference standard. The suitability of Cpd-3 as a new 5α-Rds targeting agent was investigated, both in vitro and vivo. The Cpd-3 has shown ≥98 % in vitro stability at room temperature and was remained ≥90 % stable up to 6 h. In serum Cpd-3 has revealed an analogous behavior with a small decrease in stability after 16 h. High uptake (26.25 ± 1.10 %, after 4 h of i.v.) of Cpd-3 was observed in the prostate (target tissue) of MSDR model with reasonably good target to non-target ratio. Blocking the target site with excess Cpd-2 considerably decreased the uptake of Cpd-3 to 4.10 ± 0.75 % in PCa. High in vitro stability in saline and serum and in vivo uptake in prostate of MSDR model plausibly attracts the opportunity of using Cpd-3 as a novel radiopharmaceutical for non invasive targeting of prostate.

Gallium-68-Labeled Prostate-Specific Membrane Antigen-11 PET/CT of Prostate and Nonprostate Cancers

OBJECTIVE. The purpose of this study is to provide a concise summary of the current experience with ⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA)-11 imaging of prostate and nonprostate malignancies and benign conditions. CONCLUSION. PSMA is overexpressed in prostate cancer and in the neovasculature of many other malignancies. The relevance of PSMA as a biologic target, coupled with advances in the design, synthesis, and evaluation of PSMA-based radionuclides for imaging and therapy, is anticipated to play a major role in patient care.

68Ga-PSMA-HBED-CC-Avid Synchronous Urinary Bladder Paraganglioma in a Patient With Metastatic Prostate Carcinoma

Ga-PSMA-HBED-CC PET/CT has proven to be a useful modality in patients with prostate carcinoma, especially in those with suspected recurrence and in detection of locoregional and distant metastases. However, with expanding use of this tracer, several recent reports of in vivo expression of PSMA in nonprostatic benign and malignant entities have been published. We report a patient with PSMA-avid synchronous urinary bladder paraganglioma and metastatic prostate carcinoma.

Nonspecific Uptake of 68Ga-Prostate-Specific Membrane Antigen in Diseases other than Prostate Malignancy on Positron Emission Tomography/Computed Tomography Imaging: A Pictorial Assay and Review of Literature

⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA) ligand positron emission tomography/computed tomography imaging (PET/CT) is a rapidly evolving imaging modality for prostate cancer. Many studies have proved its superiority in staging, restaging, and detecting the recurrent prostate cancer. However, case reports describing the incidental tracer uptake in benign and nonprostatic malignancies are also reported in the literature, thus questioning the specificity of the tracer. This pictorial assay illustrates the nonspecific tracer uptake encountered during PSMA PET/CT imaging, knowledge of which can increase the confidence of interpreting physicians and may also open a new path for peptide receptor radionuclide therapy in nonprostatic malignancies.