Giant Cell Tumors of the Bone: Changes in Image Features after Denosumab Administration

To assess the clinical importance in the feature change in giant cell tumors of the bone (GCTB) after denosumab treatment, detected by MRI.

In 12 patients, MRI and CT of GCTB obtained before and after the treatment retrospectively compared. The tumor size, the signal intensity (SI) ratio between the solid part of the GCTB and muscle, cystic part size, gadolinium enhancement and apparent diffusion coefficient (ADC) value were measured on MRI. The bone formation in the tumor was observed on CT and X-ray.

The mean number of denosumab injections was 19 ± 10. The follow-up period was up to 2 years. One case showed partial remission, while the other 11 cases were stable. A mean SI ratio on T₂-weighted image statistically significantly decreased from 3.9 to 1.9 after the treatment. A cystic component in the tumor was observed in five cases before the treatment, and the diameter of the cystic part decreased after the treatment in 80% of cases (4/5). All the tumors showed contrast enhancement on T₁-weighted image pre- and post-treatment (11/11). The averaged ADC values were 1.52 × 10^-3 mm²/s before and 1.44 × 10^-3 mm²/s after the treatment (P = 0.63). Bone formation in the tumor was observed in 58% of cases (7/12).

The decrease of SI ratio on T₂-weighted image, shrinkage of cystic part and bone formation should be regarded as the effectiveness of denosumab treatment despite of no substantial change in the tumor size.