Unexpected Metastatic Localizations of Prostate Cancer Determined by ⁶⁸Ga PSMA PET/CT: Series of Four Cases

Abstract

Prostate-specific membrane antigen (PSMA) is a transmembrane protein with overexpression in most prostate cancer cells. Gallium-68-(⁶⁸Ga) PSMA positron emission tomography/computed tomography (PET/CT) imaging is a game-changer in the management of prostate cancer. ⁶⁸Ga PSMA PET/CT scan is advanced and a promising radioligand has high sensitivity in determining lesions of prostate cancer with a high tumor to background ratio. The most common areas of metastasis are the bone and pelvic lymph nodes. The prognosis of prostate cancer is mainly determined by the status of metastases. The presence and the localization of metastases affects treatment planning. In our cases, we presented some examples of uncommon sites of metastases such as the brain, adrenal glands, penis and orbit. Improvements in imaging techniques, such as ⁶⁸Ga PSMA PET/CT have led to the possibility to make more determi nation of rare metastase sites in prostate cancer patients.

Figure 1.

In prostate cancer, correct evaluation of extraprostatic spread is of great importance for estimated prognosis and in treatment planning. The most common areas of metastasis are pelvic lymph nodes and bone (1). Hatzoglou et al. (2) identified the incidence of brain metastasis from prostate carcinoma as 0.16%. They also stated that non-adenocarcinoma pathology are more likely to develop brain metastasis (2). Gallium-68-(⁶⁸Ga) prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) (Philips, True Flight Select, USA) scan was performed on a 62-year-old patient with prostate adenocarcinoma (Gleason’s score 4+3, PSA 12.2 ng/mL). ⁶⁸Ga PSMA avid lesions in the right parietal (A, B, C) and thalamic (D, E, F) regions with perilesional edema were detected [maximum standardized uptake value (SUV_max): 1.3-2.6] (arrow). Magnetic resonance imaging (MRI) was performed for further evaluation. MRI report was consistent with our findings, demonstrating a 2 cm diameter mass in the right frontal lobe-precentral gyrus localization with peripheral diffusion restriction and a similar lesion in the right thalamus with a diameter of 1.3 cm. Radiotherapy was planned for cranial metastases.

Figure 2.

Metastases are the most common malignant lesions of adrenal gland. Adrenal metastasis can originate mostly from the lung (39%) and breast (35%) cancers (3). Even if the frequency of adrenal metastases was shown as 13% in an autopsy series, there are few publications in the literature with adrenal metastases of prostate cancer (4). ⁶⁸Ga PSMA PET/CT was performed in an 83-year-old patient who had prostate adenocarcinoma (Gleason’s score of 4+5, PSA 809 ng/mL). Invasive prostate lesions to seminal vesicles, bilateral adrenal masses with the largest diameter of 61x33 mm (SUV_max: 26.2) (arrow), abdominopelvic lymph nodes, and widespread sclerotic skeletal metastases with intense PSMA expression were detected. Androgen deprivation therapy and chemotherapy were started and he has been for follow-up.

Figure 3.

Secondary malignancy of the penis is a rare condition despite its rich vascularization. Tatkovic et al. (5) observed the incidence of penile metastasis of prostate cancer was 0.1% at 4860 ⁶⁸Ga PSMA PET/CT examinations. Seventy two year-old patient with prostate adenocarcinoma (Gleason’s score of 4+5) had significant PSA progression (22.6 ng/mL and 47.9 ng/Ml, respectively) despite eight cycles of chemotherapy and enzalutamide treatment. ⁶⁸Ga PSMA PET/CT revealed a large prostate mass with rectal and vesical invasion, PSMA avid inferior cervical, abdominal, and pelvic lymph nodes. Additionally, there was an intense ⁶⁸Ga PSMA expression noted in the penile shaft with a diameter of approximately 40x20 mm (SUV_max: 14.9) (arrow). Colour-coded duplex ultrasonography was used to evaluate the penile metastasis, radiotherapy was started for pencil metastasis and Lutetium-177 (¹⁷⁷Lu) PSMA was planned.

Figure 4.

More than 90% of distant metastases in prostate cancer patients are found in the bones. The axial skeleton is the most commonly affected (1). Although the osseous metastases are common in prostate cancer, orbital metastases are very rare. Adenocarcinoma of the prostate is implicated in 3.6% to 4% of all orbital metastases (6). Cranial and orbital MRI was performed on 84-year-old patient with castrate-resistant prostate cancer (PSA 17 ng/mL) who developed diplopia and proptosis in the right eye. ⁶⁸Ga PSMA PET/CT was performed upon seeing a periorbital mass in the MRI. Pathological PSMA involvement (SUV_max: 19.4) was observed in the lesion, approximately 3.5x2.5 cm in size, located in the sphenoid bone in the right and invading the temporal lobe, maxillary sinus and orbit (arrow). ⁶⁸Ga PSMA PET/CT also demonstrated multiple cervical, abdominal and pelvic nodal involvement and sclerotic skeletal metastases. 7400 MBq ¹⁷⁷Lu PSMA radionuclide therapy was administered to the patient. He did not have any side effects during treatment or in the following weeks. The patient died from posttraumatic intracranial bleeding during follow-up.