Dual-tracer positron emission tomography-computed tomography with ¹⁸F-PSMA-7Q and ¹⁸F-FDG in a patient with synchronous prostate carcinoma and undifferentiated pleomorphic sarcoma: a case description

Introduction

A unique case of prostate cancer (PCa) synchronous with undifferentiated pleomorphic sarcoma was treated, for which dual-tracer [fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) and fluorine-18-labeled prostate-specific membrane antigen-7Q (¹⁸F-PSMA-7Q)] positron emission tomography-computed tomography (PET/CT) was pivotal for differentiation. Although ¹⁸F-FDG PET/CT is the standard modality for sarcoma staging, its utility in PCa is limited, while the converse is true for ¹⁸F-PSMA-7Q PET/CT (1-4). The distinctive “flip-flop” pattern of tracer avidity enabled clear discrimination between the metastases from two different origins and helped guide subsequent management.

The case highlights the significant diagnostic value of employing dual tracers in patients with suspected synchronous malignancies, as this can provide critical information that a single imaging modality would miss.

Case presentation

A 79-year-old male with suspected recurrence of undifferentiated pleomorphic sarcoma in the left upper arm and retroperitoneal lymphadenopathy identified on CT underwent ¹⁸F-FDG PET/CT for staging evaluation (Figure 1A). The administered activities of both ¹⁸F-FDG and ¹⁸F-PSMA-7Q were 359 MBq (3.7 MBq/kg body weight; patient weight: 97 kg). PET/CT imaging was performed with a uMI Panorama 28C PET/CT scanner (United Imaging, Shanghai, China). For ¹⁸F-FDG PET/CT, the patient fasted for at least 6 hours before intravenous injection, and images were acquired 60 minutes postinjection. For ¹⁸F-PSMA-7Q PET/CT, no special preparation was required, and images were acquired 90 minutes postinjection. All raw images were reconstructed with iterative reconstruction algorithms to obtain PET, CT, and PET/CT fusion images in the axial, coronal, and sagittal planes with a slice thickness of approximately 3 mm. All images were interpreted by two experienced nuclear medicine physicians.

Figure 1 ¹⁸F-FDG and ¹⁸F-PSMA-7Q PET/CT images of the patient. (A) Maximum intensity projection of ¹⁸F-FDG PET. (B) CT and corresponding PET/CT fusion images of the left arm lesion. (C) CT and corresponding PET/CT fusion images of the prostate. (D) CT and corresponding PET/CT fusion images of the pelvic lymph nodes. (E) CT and corresponding PET/CT fusion images of the acetabulum. (F) Maximum intensity projection of ¹⁸F-PSMA-7Q PET. (G) CT and corresponding PET/CT fusion images of the left arm lesion. (H) CT and corresponding PET/CT fusion images of the prostate. (I) CT and corresponding PET/CT fusion images of the pelvic lymph nodes. (J) CT and corresponding PET/CT fusion images of the acetabulum. (A,F) The black arrow indicates the arm lesion, and the white arrows indicate the metastatic lymph nodes and skeletal lesion. (B,G) The arrows indicate the arm lesion. (C,H) The arrows indicate the prostate. (D,I) The arrows indicate the largest lymph node located medial to the right pelvic wall. (E,J) The arrows indicate the osteolytic lesion at the right acetabulum. ¹⁸F-FDG, fluorine-18 fluorodeoxyglucose; ¹⁸F-PSMA-7Q, fluorine-18-labeled prostate-specific membrane antigen-7Q; CT, computed tomography; PET, positron emission tomography.

The PET/CT scan demonstrated intense FDG uptake in the left arm lesion (Figure 1A,1B), with a maximum standardized uptake value (SUVmax) of 9.5. Incidentally, mildly increased FDG metabolism was noted in the prostate and seminal vesicles, with an SUVmax of 2.3 (Figure 1C). Multiple mildly FDG-avid lymph nodes were observed in the retroperitoneal and pelvic regions, with the largest located medial to the right pelvic wall (SUVmax =3.1) (Figure 1D). Additionally, there was a mild increase in FDG uptake in the osteolytic lesions at the right acetabulum, posterior aspect of the first rib, and the right transverse process of the second thoracic vertebra (SUVmax =4.7) (Figure 1E). The patient’s serum prostate-specific antigen (PSA) level was 114.00 ng/mL. Digital rectal examination revealed a markedly enlarged prostate with diffuse induration, loss of the median sulcus, and ill‑defined borders, suggesting extensive tumor replacement. No blood was noted on the glove. The findings from baseline laboratory tests before treatment were as follows: free PSA =11.40 ng/mL (reference 0–1 ng/mL), total PSA =114.00 ng/mL (reference 0–4 ng/mL), testosterone =3.07 ng/mL (reference 1.75–7.51 ng/mL), and an unremarkable complete blood count. The multidisciplinary team considered the possibility of synchronous PCa with metastasis. For further evaluation, the patient underwent ¹⁸F-PSMA-7Q PET/CT examination. Meanwhile, the lesion in the left arm also demonstrated moderate PSMA uptake (Figure 1F) although its avidity was significantly lower than that observed in other lesions (SUVmax =7.6) (Figure 1G). The examination revealed markedly increased PSMA uptake in the prostate and left seminal vesicle (SUVmax =37.6) (Figure 1H). Significantly elevated PSMA uptake was also observed in the retroperitoneal and pelvic lymph nodes, with pronounced uptake in the larger node medial to the right pelvic wall (SUVmax =20.0) (Figure 1I). Additionally, intense PSMA uptake was noted in the right acetabulum, posterior aspect of the first rib, and the right transverse process of the second thoracic vertebra (SUVmax =22.9) (Figure 1F,1J).

The patient subsequently underwent amputation of the left upper limb (Figure 2A). Postoperative biopsy of the arm mass confirmed recurrent undifferentiated pleomorphic sarcoma (Figure 2B). Prostate biopsy confirmed PCa. Specifically, pathological examination of the left prostatic lobe showed acinar adenocarcinoma with a Gleason score of 4+3=7, while biopsy of the right lobe revealed acinar adenocarcinoma with a Gleason score of 4+4=8 (Figure 2C,2D).

Figure 2 Intraoperative and pathological images of the patient. (A) Intraoperative photograph of the patient’s left arm. (B) Pathological image of the biopsy tissue from the lesion site after amputation (hematoxylin and eosin staining). (C) Pathological image of the patient’s prostate biopsy tissue (hematoxylin and eosin staining). (D) Immunohistochemical image of the patient’s prostate biopsy tissue.

Based on the PET/CT findings and pathological diagnoses, the patient received treatment for both malignancies. For PCa, the patient was diagnosed with low-volume metastatic hormone-sensitive PCa (mHSPC). He was started on androgen deprivation therapy (ADT) with goserelin in combination with enzalutamide. For the undifferentiated pleomorphic sarcoma, given that postoperative pathology confirmed complete resection but ruled out lymph node or distant metastasis, no systemic chemotherapy was administered. The sarcoma was managed with surgical resection alone. Approximately 1 month after the initiation of ADT combined with enzalutamide, laboratory tests indicated a significant response: free PSA decreased to 0.279 ng/mL, total PSA to 1.150 ng/mL, and testosterone to 0.34 ng/mL, and the complete blood count was normal.

All procedures in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

PSMA is known to be overexpressed in both primary and metastatic PCa (5). PSMA PET/CT is now widely used for staging intermediate-to-high-risk PCa and evaluating patients with biochemical recurrence (6). Moreover, PSMA PET/CT has emerged as a valuable tool for diagnosing “clinically significant” PCa via targeted biopsy. A prospective study by Pepe et al. showed that PSMA PET/CTguided targeted biopsy missed only 4.5% of clinically significant PCa cases, while multiparametric magnetic resonance imaging (MRI)-guided biopsy missed 18.1%, with the diagnostic accuracy being 77.5% and 73.7%, respectively. This confirmed that PSMA PET/CT is not inferior to multiparametric MRI and can improve the detection of clinically significant PCa (7). PSMA expression in nonprostatic malignancies has also been reported in the literature (8-10). Recent studies have further indicated that PSMA can be expressed in the neovascular endothelium of sarcomas (4,11). Our case represents a rare example of dual primary malignancies, namely PCa and undifferentiated pleomorphic sarcoma. The two primary tumors and their metastatic lesions demonstrated uptake of both ¹⁸F-FDG and ¹⁸F-PSMA-7Q, and the tracer uptake intensities (SUVmax) between the two malignancies were distinct.

PSMA, a transmembrane glutamate carboxypeptidase II encoded by the folate hydrolase 1 (FOLH1) gene (12), is expressed in the neovasculature of sarcoma tissues, albeit at levels significantly lower than those in PCa and its metastatic lesions (13). This differential expression of FOLH1 likely accounts for the marked disparity in tracer uptake intensity observed between the two types of lesions. On this basis, the PSMA-avid skeletal and soft-tissue lesions, but not the arm lesion, were considered consistent with metastatic PCa. In patients suspected of having concurrent PCa metastases and another malignancy, dual-tracer (¹⁸F-PSMA-7Q and ¹⁸F-FDG) PET/CT can provide valuable differential diagnostic information and help guide subsequent management (14). In our case, the reversal of tracer avidity across metastatic sites aided in distinguishing the origin of the metastases, thereby informing subsequent treatment planning.

Indeed, the dual-tracer PET/CT results directly impacted treatment. By confirming that all lymph node and bone metastases originated from PCa, we could spare the patient from systemic therapy for sarcoma after amputation. Additionally, ¹⁸F-PSMA-7Q PET/CT indicated the PCa to be low-volume mHSPC, and thus ADT (goserelin) combined with enzalutamide was administered.

Although PSMA PET/CT has greatly improved PCa management, prostatic ductal adenocarcinoma is a special entity with a nonnegligible falsenegative rate due to low PSMA expression (15-17). Thus, nuclear medicine physicians should check for a prostatic ductal adenocarcinoma component in pathology, interpret PSMA PET/CT cautiously, and consider performing ¹⁸F-FDG imaging when needed. Although our patient had pure acinar adenocarcinoma, this theoretical scenario supports the value of dual‑tracer PET/CT in atypical cases.

Conclusions

Dual-tracer ¹⁸F-FDG and ¹⁸F-PSMA-7Q PET/CT enabled accurate differentiation of metastatic lesions in a patient with synchronous PCa and undifferentiated pleomorphic sarcoma, underscoring its value for lesion attribution and clinical decision-making in complex dual-malignancy settings.

Acknowledgments

We would like to thank the Nuclear Medicine Department of Affiliated Jinan Third People’s Hospital of Jining Medical University for their assistance in performing the PET/CT scans and for their technical support in interpreting the results. We also acknowledge the contributions of the multidisciplinary team involved in the patient’s care.

Footnote

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0310/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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