PSMA-avid rib lesions in prostate cancer patients: differentiating false positives from metastatic disease

Prostate-specific membrane antigen (PSMA)-PET/CT has become integral to management of prostate cancer; however, PSMA-avid rib lesions pose a diagnostic challenge. This study investigated clinicopathological and imaging findings that predict metastatic etiology of PSMA-avid rib lesions.

Consecutive patients with prostate cancer that underwent PET/CT with [¹⁸F]F-DCFPyL in 2021-2023 for newly diagnosed intermediate-/high-risk prostate cancer or recurrent/metastatic disease and had PSMA-avid rib lesions were included. Imaging findings assessed were: lesion number, PSMA expression (maximum standard uptake value (SUV_max), miPSMA score), CT features (sclerotic, lucent, fracture, no correlate), other sites of metastases, and primary tumor findings. A composite reference standard for rib lesion etiology (metastatic vs non-metastatic) based on histopathology, serial imaging, and clinical assessment was used.

One hundred and seventy-five men (median 71 years, IQR 65-77) with PSMA-avid rib lesions were included; 47/175 (26.9%) had rib metastases. Only 1/47 (2.1%) of these patients had isolated rib metastasis without PSMA-avid metastases in other bones, nodes, or visceral organs; the other 46/47 (97.9%) patients with rib metastases also had other sites of PSMA-avid disease. Patients with rib metastases were older, had higher prostate-specific antigen levels, and higher-grade tumors (p < 0.01). Metastatic rib lesions had higher uptake (SUV_max, miPSMA), more commonly involved multiple ribs, and were more often sclerotic (p < 0.01); lucency/fractures were only seen in benign lesions.

Several imaging and clinicopathological factors differed between PSMA-avid metastatic and benign lesions. Isolated rib lesions without other sites of metastasis are almost always benign. Careful assessment of CT features can help diagnose benign lesions.

Question While prostate-specific membrane antigen (PSMA)-PET/CT has become integral to the management of prostate cancer, PSMA-avid rib lesions pose a diagnostic challenge. Findings Approximately a quarter of patients who had PSMA-avid rib lesions were metastatic. However, only 2.1% of them had isolated rib metastasis (without PSMA-avid metastases elsewhere). Clinical relevance Isolated PSMA-avid rib lesions are almost always benign when there is no evidence of metastatic disease elsewhere. Scrutinizing CT features can help diagnose benign PSMA-avid lesions with greater certainty.