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

OBJECTIVES

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.

MATERIALS AND METHODS

Consecutive patients with prostate cancer that underwent PET/CT with [F]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), 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.

RESULTS

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, miPSMA), more commonly involved multiple ribs, and were more often sclerotic (p < 0.01); lucency/fractures were only seen in benign lesions.

CONCLUSION

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.

KEY POINTS

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.