Prostate-specific Membrane Antigen Imaging in Recurrent Medullary Thyroid Cancer: A New Theranostic Tracer in the Offing?

⁶⁸Ga prostate-specific membrane antigen (PSMA)-positron emission tomography/computed tomography (PET/CT) is commonly used in the management of patients with prostate cancer. This scan has a theranostic role in a selected group of patients as of date. However, PSMA expression has also been reported previously in other malignancies such as breast, bladder, gastric, colon, renal cell carcinoma, rectum, lung, hepatocellular carcinoma, multiple myeloma, and follicular lymphoma and in some nonneoplastic conditions.[12345678] Few studies have shown expression of PSMA in thyroid cancer.[910111213] ¹⁷⁷Lu/ ⁹⁰Y DOTATATE therapy has been used previously in metastatic medullary thyroid cancer (MTC).[1415] Few earlier studies have reported PSMA expression in the endothelium of tumor neovasculature where there is abnormal protein expression and increased transcription of PSMA through activation of the transcriptional enhancer region in endothelial cells.[16] This 68-year-old man with MTC, who earlier underwent total thyroidectomy and left neck dissection as primary surgery and left modified radical neck dissection and radiotherapy for nodal recurrence, had persistently rising calcitonin (doubling time of ~9 months, raised from 36 to 107 ng/mL) and carcinoembryonic antigen level (27 ng/mL). He had recurrence for the second time, and options of surgery and radiotherapy were already exhausted. Option of using vandetanib/cabozantinib was unavailable. The patient also had a negative metaiodobenzylguanidine (MIBG) scan and somatostatin receptor PET/CT [Figure 1b and e], which ruled out ¹³¹I MIBG and ¹⁷⁷Lu DOTATATE therapy. To explore the possibility of using ¹⁷⁷Lu-DKFZ-PSMA 617 therapy, he underwent a ⁶⁸Ga-PSMA PET/CT, which showed soft-tissue density lesion in the left paratracheal region, extending into tracheoesophageal groove with increased PSMA uptake [Figure 1c and f] “SUVmax-19.7, SUVmax liver-8.0”. The same mass was fluorodeoxyglucose positive [Figure 1a] but showed no significant uptake on ⁶⁸Ga DOTANOC uptake [Figure 1b and e]. Further studies will help ascertain the utility of ¹⁷⁷Lu-PSMA-DKFZ-617 in such patients with exhausted treatment options.

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Figure 1 Maximum intensity projection images of ¹⁸F-fluorodeoxyglucose (a), 68Ga-DOTANOC (b), ⁶⁸Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (c), revealing increased uptake of ¹⁸F-fluorodeoxyglucose and ⁶⁸Ga prostate-specific membrane antigen in the left paratracheal recurrent soft-tissue lesion, but no significant uptake on scan and somatostatin receptor positron emission tomography/computed tomography (thin black arrow). Axial computed tomography (d), fused ⁶⁸Ga-DOTANOC (e), and ⁶⁸Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (f) images reveal soft-tissue density lesion in the left paratracheal region, extending into tracheoesophageal groove (d) with increased prostate-specific membrane antigen uptake (black arrow, “SUVmax-19.7, SUVmax liver-8.0”)

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