Assessment of Malignancy and PSMA-expression of Uncertain Bone Lesions in [18F]PSMA-1007 PET/CT for Prostate Cancer- a Single Centre Experience of PET-guided Biopsies

Abstract

Purpose: Uncertain bone lesions (UBL) with intensive radiopharmaceutical avidity are frequently observed in patients undergoing [18F]PSMA-1007 PET/CT for the detection of prostate cancer (PC). Such lesions can pose diagnostic conundrums and risk an incorrect staging. The aim of this short communication is to share the results of PET-guided biopsies of such lesions. Methods: A retrospective analysis revealed 10 patients who were referred to our department for PET-guided biopsy of UBL visible in a previous [18F]PSMA-1007 PET/CT. [18F]-PSMA-1007 PET-guided biopsy was conducted for 11 PSMA-avid bone lesions in these 10 patients. The biopsy materials were analysed for tissue typing and immunohistochemistry (IHC) was performed for prostate-specific-membrane-antigen (PSMA) expression. The scans were analysed by two experienced physicians in a consensus read for clinical characteristics and radiopharmaceutical uptake of lesions. Results: 1/11 (9.1%) of the lesions biopsied was confirmed as bone metastasis of PC with intense PSMA-expression while 10/11 (90.9%) lesions were revealed to be unremarkable bone tissue without evidence of PSMA-expression at IHC. Amongst all bone lesions assessed by biopsy, eight were visually classified as being at high risk of malignancy in the PET/CT (SUVmean 12.0 ± 8.1; SUVmax 18.8 ± 13.1), three as equivocal (SUVmean 4.6 ± 2.1; SUVmax 7.2 ± 3.0) and zero as low risk. No UBL had any CT correlate. Conclusions: In this cohort biopsy revealed that a small but relevant number of UBL are true metastases. For those confirmed as benign, no PSMA-expression at IHC was observed, suggesting a non-PSMA mediated cause for intensive [18F]PSMA-1007-uptake of which the reason remains unclear. Readers must interpret such lesions with caution in order to reduce the risk of erroneous staging and subsequent treatment. PET-guided biopsy, particularly in the absence of morphological changes in the CT, can be a useful method to clarify such lesions.