Bone Metastases and Skeletal-Related Events in Medullary Thyroid Carcinoma.

Context: Bone metastases (BM) can lead to devastating skeletal-related events (SREs) in cancer patients. Data regarding medullary thyroid carcinoma (MTC) with BM are lacking.
Objective: We evaluated the natural history of BM and SREs in MTC patients identified by a cancer center tumor registry.
Setting: The study was conducted at a tertiary cancer center.
Patients and Main Outcome Measures: We retrospectively reviewed the charts of MTC patients with BM who received care from 1991 to 2014 to characterize BM and SREs.
Results: Of 1008 MTC patients treated, 188 were confirmed to have BM (19%), of whom 89% (168 of 188) had nonosseous distant metastases. Median time from MTC to BM diagnosis was 30.9 months (range 0-533 mo); 25% (45 of 180) had BM identified within 3 months of MTC diagnosis. Median follow-up after detecting BM was 1.6 years (range 0-23.2 y). Most patients (77%) had six or more BM lesions, most often affecting the spine (92%) and pelvis (69%). Many patients (90 of 188, 48%) experienced one or more SREs, most commonly radiotherapy (67 of 90, 74%) followed by pathological fracture (21 of 90, 23%). Only three patients had spinal cord compression. Patients with more than 10 BM lesions were more likely to experience SREs (odds ratio 2.4; P = .007), with no difference in 5-year mortality after MTC diagnosis between patients with (31%) and without SREs (23%) (P = .11).
Conclusions: In this large retrospective series, BM in MTC was multifocal, primarily involving the spine and pelvis, supporting screening these regions for metastases in at-risk patients. SREs were common but spinal cord compression was rare. Antiresorptive therapies in this population should be investigated further with prospective trials.