Epidural tumor pseudoprogression after spine SBRT: A case report and a mini review of the literature

Introduction: Stereotactic body radiotherapy (SBRT) to the spine is becoming a more common form of treatment. Response assessment is challenging because pseudoprogression (PP) is difficult to distinguish from true tumor progression (TTP). Methods: We report the case of a patient with anaplastic thyroid carcinoma and a bony metastasis to T-7. The MRI 22 months after the first SBRT to this location showed radiological tumor progression to the epidural space resulting in a re-SBRT. The three and six months MRI after re-SBRT showed again progressive epidural growth. After T-7 vertebrectomy, obtained tissue specimens were histopathologically evaluated. Results: Although the MRI sequences after second SBRT were highly suspicious of tumor progression into epidural space, only a small cluster of carcinoma cells of 1mm diameter was found within the bony structure near the disc, not belonging to the radiologically highly suspicious epidural mass. Conclusion: To our knowledge, we report the first case of a radiographic tumor progression to the epidural space following primary SBRT and re-SBRT, which histopathologically revealed a PP after spine surgery. Based on the “epidural progression criterion” from the SPINO-consensus, the first and the second progression after SBRT should have been classified as TTP. Due to the challenge in distinguishing TTP from PP, reporting of such cases are essential to share experiences and thereby improve the understanding of PP after spine SBRT.