Histopathological Findings After Reirradiation Compared to First Irradiation of Spinal Bone Metastases With Stereotactic Body Radiotherapy: A Cohort Study.

BACKGROUND

Stereotactic body radiotherapy (SBRT) of the spine provides superior tumor control, but vertebral compression fractures are increased and the pathophysiological process underneath is not well understood. Data on histopathological changes, particularly after salvage SBRT (sSBRT) following conventional irradiation, are scarce.

OBJECTIVE

To investigate surgical specimens after sSBRT and primary SBRT (pSBRT) regarding histopathological changes.

METHODS

We assessed 704 patients treated with spine SBRT 2006 to 2012. Thirty patients underwent salvage surgery; 23 histopathological reports were available. Clinical and histopathological findings were analyzed for sSBRT (69.6%) and pSBRT (30.4%).

RESULTS

Mean time to surgery after sSBRT/pSBRT was 8.3/10.3 mo (P = .64). Reason for surgery included pain (sSBRT/pSBRT: 12.5%/71.4%, P = .25), fractures (sSBRT/pSBRT: 37.5%/28.6%, P = .68), and neurological symptoms (sSBRT/pSBRT: 68.8%/42.9%, P = .24). Radiological tumor progression after sSBRT/pSBRT was seen in 71.4%/42.9% (P = .2). Most specimens displayed viable/proliferative tumor (sSBRT/pSBRT: 62.5%/71.4%, P = .68 and 56.3%/57.1%, P = .97). Few specimens showed soft tissue necrosis (sSBRT/pSBRT: 20%/28.6%, P = .66), osteonecrosis (sSBRT/pSBRT: 14.3%/16.7%, P = .89), or bone marrow fibrosis (sSBRT/pSBRT: 42.9%/33.3%, P = .69). Tumor bed necrosis was more common after sSBRT (81.3%/42.9%, P = .066). Radiological tumor progression correlated with viable/proliferative tumor (P = .03/P = .006) and tumor bed necrosis (P = .03). Fractures were increased with bone marrow fibrosis (P = .07), but not with osteonecrosis (P = .53) or soft tissue necrosis (P = .19). Neurological symptoms were common with radiological tumor progression (P = .07), but not with fractures (P = .18).

CONCLUSION

For both, sSBRT and pSBRT, histopathological changes were similar. Neurological symptoms were attributable to tumor progression and pathological fractures were not associated with osteonecrosis or tumor progression.