Supplementary Material for: Case series: ‘silent’ spinal epidural metastases in metastatic castrate resistant prostate cancer

Introduction: Spinal epidural metastases (SEM) is an uncommon phenomenon and traditionally occurs as a pre-terminal event in heavily pre-treated patients. The introduction of novel anti-androgen therapies, such as enzalutamide and abiraterone acetate, has greatly improved the survival of patients with metastatic prostate cancer but may be changing the pattern of disease. Case presentation: Four patients diagnosed with metastatic castrate-resistant prostate cancer (CRPC) were commenced on enzalutamide prior to chemotherapy. Baseline scans in all patients demonstrated extensive bony disease and lymph node involvement. All patients experienced a moderate initial PSA response to treatment (median PSA at baseline 53.5ng/mL to median nadir 24.5ng/mL). In all four cases, clinical presentation of spinal cord compression was unexpected with no prodromal neurological symptoms, PSA levels either stable or slowly rising, and CT scans and whole-body bone scans showing stable disease at other metastatic sites. Whole spine MRI on presentation of neurological deficits showed epidural and dural metastases on the background of stable bone disease. Spinal cord compression occurred at a median 11.4 months after starting enzalutamide. Conclusion: Clinicians should be aware of this change in the pattern of CRPC in patients treated with novel antiandrogen therapy. Onset of ‘silent’ spinal cord compression due to SEM rather than bone metastases, can occur relatively early with minimal warning despite stable disease on PSA and standard imaging. Differential progression in non-traditional sites suggests that research into the androgen microenvironment in a wide range of tissue sites should be undertaken, and may explain why prostate cancer metastasizes preferentially to bone and lymph nodes.