Purpose: The purpose of this study was to clarify the significance of positron emission tomography (PET) and computed tomography (CT) findings for evaluating the bone metastasis of breast cancer during therapy.
Patients and methods: Forty-seven patients with bone metastases from breast cancer who underwent sequential FDG-PET/CT studies during therapy were enrolled. A total of 771 lesions were identified. The changes in the PET and CT findings were compared with the tumor marker levels in each patient by calculating the weighted kappa value. The correlation between the PET and CT findings was examined for each lesion by an adjusted Chi-square test.
Results: The change in the tumor marker levels was substantially correlated with the PET findings and moderately correlated with the CT findings (weighted kappa = 0.780 and 0.585 for quadratic weighting, respectively). An increase in FDG uptake was correlated with lytic changes on the CT images (62/65, 95.4 %, p < 0.05). Sclerotic changes suggested improvement, but sclerosis and progression occurred at the same time in some lesions.
Conclusion: Changes of FDG uptake are useful for evaluating individual bone metastases in cases of breast cancer during therapy. Lytic change on CT images suggests progression of bone metastasis. The lysis-progression/sclerosis-improvement pattern was observed in the majority of subjects, but a sclerosis-progression pattern was also observed. The hybrid pattern of increase of FDG uptake on PET/lytic change on CT is most accurate to show progression of bone metastases. Assessments of these processes during therapy are necessary for the precise evaluation of bone metastases.