Paraganglioma as a risk factor for bone metastasis.

Malignant pheochromocytoma (PHEO) and paraganglioma (PGL) (PHEO and PGL: PPGL) are frequently associated with bone metastasis. Bone metastasis requires long-term management and may lead to skeletal-related events (SREs) that remarkably reduce patients' quality of life (QOL). The aim of this study was to elucidate the risk factors for developing bone metastasis in patients with PPGL. The medical records of 40 consecutive adult patients with malignant PPGL at the National Hospital Organization Kyoto Medical Center between 2006 and 2016 were reviewed. SREs were defined as pathologic fracture, spinal cord compression, and the need for bone irradiation and/or surgery. PHEO (20/40) and PGL (20/40) were each present in 50% of the patients. Bone was the most frequent site of metastasis, detected in 60% (24/40). Bone metastasis was more frequent in patients with PGL (16/20, 80%) than in patients with PHEO (8/20, 40%) (p = 0.02). Half (12/24) of the patients with bone metastasis had at least one SRE. Extra-skeletal invasion of the spine, defined as local infiltration to the surrounding tissue beyond the cortical bone, was more frequently observed in patients with bone metastasis associated with SREs than without them (p = 0.001). Careful follow-up and management are warranted especially in patients with PGL as a risk factor for bone metastasis and with extra-skeletal invasion of the spine as risk factor of SREs.