Solitary rib lesions showing prostate‐specific membrane antigen (PSMA) uptake in pre‐treatment staging ⁶⁸Ga‐PSMA‐11 positron emission tomography scans for men with prostate cancer: benign or malignant?

Abstract

Objectives To determine the proportion of solitary rib lesions on pre‐treatment 68Gallium‐labelled prostate‐specific membrane antigen (PSMA)/computed tomography (CT) scans in men with prostate cancer that are malignant and examine any predictive factors. Patients and methods This retrospective single tertiary referral institution cohort study of men reviewed the results of 68Ga‐PSMA‐11 positron emission tomography (PET)/CT scans performed for primary staging prior to treatment of prostate cancer from July 2014 to September 2019. Men with PSMA uptake outside the prostate in only the rib lesion were included. A solitary rib lesion was considered to be malignant if it increased in size on follow‐up imaging. A lesion was considered benign if the prostate‐specific antigen (PSA) level remained <0.1 µg/L following a radical prostatectomy (RP), <2 µg/L above nadir following radiotherapy (RT) as per the Phoenix criteria, histology was benign on rib biopsy, or follow‐up imaging showed no growth of the rib lesion. If a lesion did not meet these criteria it was considered indeterminate. Results A total of 62 men had PSMA uptake in a solitary rib lesion; 54 went on to have RPs and eight underwent RT. In all, 61 of the men (98.4%) met the criteria for a benign rib lesion. Only one man had a false‐negative malignant lesion. This man had a rib lesion with a low maximum standardised uptake value (SUVmax) of 2.21 reported as benign, but the postoperative PSA level was 0.67 µg/L and the rib lesion progressed on follow‐up imaging, with development of widespread metastases. Of the benign rib lesions, there were four false positives reported as possible metastases. Three had percutaneous rib biopsies, two of which came back with benign histology and one was indeterminate. The indeterminate biopsy patient had a RP and his postoperative PSA level was <0.1 µg/L. A total of 43 (69.4%) men with benign rib lesions had a SUVmax greater than the SUVmax of the malignant lesion. Conclusion To our knowledge, this is the first cohort study of men with PSMA‐avid solitary rib lesions on pre‐treatment 68Ga‐PSMA PET/CT staging scans for prostate cancer. Our results indicate that the vast majority of these lesions have low‐intensity uptake and are benign. Intervention to confirm this is not usually required.

Bone Uptake in Prostate Cancer Patients

“…Conversely, shoulder girdle and sternal lesions were mostly malignant with 6 PCa metastases out of 7 lesions (85.7%). This is in agreement with the retrospective study by Chen et al 29 where the authors found that 98.4% of the solitary costal bone uptake at PSMA PET/CT during initial staging were benign, as confirmed by PSA negativation after radical prostatectomy. These patterns are consistent with the natural history of PCa.…”

PET/CT with &lt;sup&gt;18&lt;/sup&gt;F-PSMA in Patients with Prostate Cancer, Review of the Initial Experience

“…In our initial experience, we considered these uptakes as nonspecific, however there was no significant change in size and SUVlmax at follow-up. There is little literature that mentions the nature of these solitary uptake in ribs, however we identified that most of them are of benign origin; taking into account the low uptake of the radiopharmaceutical, the correlation with any signs of trauma and PSA levels [25].…”

False Positive Findings of [18F]PSMA-1007 PET/CT in Patients After Radical Prostatectomy with Undetectable Serum PSA Levels

“…Only 2 patients had corresponding CT findings. Chen et al have reported that 98.4% of the solitary [ 68 Ga] PSMA-11-avid rib foci were benign (19). In a recent retrospective study, the rate of non-specific bone lesions (NSBLs) among PC patients in [ 18 F]PSMA-1007 PET/CT was analyzed (20).…”