Purpose: Brain-metastatic prostate adenocarcinoma is a rare phenomenon, accounting for 1.6% of all prostate cancer metastases (Tremont-Lukats et al. 2003). Solitary parenchymal metastases without intervening nodal or osseous metastases are particularly rare. The 68Ga-PSMA-11 PET has been heavily validated for staging of prostate cancer and detection of biochemical recurrence (Hope et al. 2019). However, multiple non-prostate histologies demonstrate increased uptake of 68Ga-PSMA (de Galiza Barbosa et al. 2020). This introduces uncertainty regarding the etiology and treatment of these lesions without pathologic confirmation. Here, we present a case of brain-metastatic prostate adenocarcinoma identified on PSMA-PET and successfully treated with stereotactic Gamma Knife Radiosurgery (GKRS), to emphasize the need for tissue acquisition to confirm the diagnosis and appropriate treatment regimen.
Methodology: A 70 year-old male, with history of stage pT3aN0M0, Gleason 4+5=9 prostate adenocarcinoma s/p radical prostatectomy and salvage prostatic fossa irradiation, presented with biochemically recurrent disease. He underwent PSMA PET, which identified a focus of activity fusing to the left occipital lobe without non-contrasted CT correlate. High resolution MRI brain imaging revealed a solitary 9.5 mm peripherally enhancing parenchymal lesion with surrounding vasogenic edema.
Results: The patient underwent left occipital craniotomy and tumor resection, and surgical pathology was confirmed as metastatic prostate adenocarcinoma. At 1 month post-resection, the patient underwent GKRS; the tumor bed and two additional metastases identified on thin-cut MRI (1 mm) each received 24 Gy prescribed to the 50% isodose line (maximum dose of 48 Gy). He was initiated on androgen deprivation therapy 2 weeks after GKRS and repeat MRI scan at 6 months post-radiation revealed decreased size of the treated lesion, without new pathologic enhancement to suggest disease recurrence.
Conclusions: Brain-metastatic prostate adenocarcinoma without nodal or osseous metastases is a rare situation. Although PSMA PET effectively localizes metastases, including intracranial lesions, its affinity for non-prostate histologies introduces a degree of uncertainty into the diagnostic process, prompting the need for more invasive procedures for pathologic confirmation. Herein, we report successful histologic diagnosis of a brain-metastatic prostate lesion and GKRS delivery as a safe, efficacious treatment that confers excellent durable control as part of a multi-therapy regimen. This case emphasizes the need to incorporate clinical, radiographic, and histopathologic data to distinguish between common and rare disease presentations and identify appropriate, safe, and effective treatment regimens for brain metastatic cancer patients.
References: Tremont-Lukats, I.W., et al. (2003). Brain Metastasis from Prostate Carcinoma: The M.D. Anderson Cancer Center Experience. Cancer, 98 (2): 363-368. https://doi.org/10.1002/cncr.11522. Hope, T.A., et al. (2019). Metaanalysis of 68Ga-PSMA-11 PET Accuracy for the Detection of Prostate Cancer Validated by Histopathology. J Nucl Med., 60 (6): 786-793. https://doi.org/10.2967/jnumed.118.219501. de Galiza Barbosa, et al. (2020). Nonprostatic diseases on PSMA PET imaging: a spectrum of benign and malignant findings. Cancer Imaging, 20: 1-23. https://doi.org/10.1186/s40644-020-00300-7.
