• Jabehdar Maralani Pejman P Department of Medical Imaging, University of Toronto, Toronto, Canada., Kathleen Winger, Sean Symons, Matylda Machnowska, Chinthaka Heyn, Ali Helmi, Aimee Chan, Chia-Lin Tseng, and Arjun Sahgal.
• Department of Medical Imaging, University of Toronto, Toronto, Canada.
• Neurosurgery. 2019 Mar 1; 84 (3): 647-654.

BackgroundTumor osseous pseudoprogression (PP), defined as an imaging-based transient increase in tumor size following treatment, was recently described in patients with spinal metastases following stereotactic body radiation therapy. Distinguishing PP from true tumor progression is critical.ObjectiveTo describe the incidence, time of onset, and time range of PP following stereotactic body radiation therapy in patients treated for spinal metastases from either prostate cancer (PC) or renal cell carcinoma (RCC), and associated predictive factors.MethodsA retrospective study was conducted on our institution's cancer database from 2009 to 2015. Selection was based on single level, no prior radiation or surgery, ≥2 follow-up spine magnetic resonance imaging (MRI), and metastases arising from either PC or RCC. Gross tumor volume was contoured on pre- and up to 5 posttreatment MRIs. Patients were sorted into groups depending on gross tumor volume response: PP, non-PP, or progressive disease. Clinical and dosimetric variables were compared using either Fisher's exact test or Kruskal-Wallis analyses.ResultsForty-three spinal segments from 31 patients were analyzed. RCC and PC patients showed similar incidence of PP (∼37%). Whether the primary was lytic or sclerotic was a significant predictive factor with more PP in the lytic group (P = .0208). There was a trend of earlier PP onset in RCC (within 6-18 mo) as compared to PC; however, PC segments showed more time-confined presentation of PP (9-12 mo).ConclusionThere was a higher incidence of PP in lytic compared to sclerotic primary tumor type. PP in spinal metastatic sites may have variable presentations depending on the primary cancer.Copyright © 2018 by the Congress of Neurological Surgeons.

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