Pitfalls of FDG-PET for the diagnosis of osteoblastic bone metastases in patients with breast cancer

Purpose: The purpose of this study was to investigate the pitfalls of using 2-[F-18]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) for the evaluation of osteoblastic bone metastases in patients with breast cancer by comparing it with Tc-99m-hydroxymethylene diphosphonate bone scintigraphy. Methods: Among the 89 breast cancer patients (mean age 59 +/- 15 years) who had undergone both FDG-PET and bone scintigraphy within 1 month between September 2003 and December 2004, 55 with bone metastases were studied. The bone metastases were visually classified by multi-slice CT into four types according to their degree of osteosclerosis and osteolysis-osteoblastic, osteolytic, mixed and invisible-and compared in terms of tracer uptake on FDG-PET or bone scintigraphy and SUVmean on FDG-PET. Differences in the rate of detection on bone scintigraphy and FDG-PET were analysed for significance by the McNemar test. Results: The sensitivity, specificity and accuracy of bone scintigraphy were 78.2%, 82.4% and 79.8% respectively, and those of FDG-PET were 80.0%, 88.2% and 83.1%, respectively, revealing no significant differences. According to the CT image type, the visualisation rate of bone scintigraphy/FDG-PET was 100%/55.6% for the blastic type, 70.0%/100.0% for the lytic type, 84.2%/94.7% for the mixed type and 25.0%/87.5% for the invisible type. The visualisation rates of bone scintigraphy for the blastic type and FDG-PET for the invisible type were significantly higher. The SUVmean of the blastic, lytic, mixed and invisible types were 1.72 +/- 0.28, 4.14 +/- 2.20, 2.97 +/- 1.98 and 2.25 +/- 0.80, respectively, showing that the SUVmean tended to be higher for the lytic type than for the blastic type. Conclusion: FDG-PET showed a low visualisation rate in respect of osteoblastic bone metastases. Although FDG-PET is useful for detection of bone metastases from breast cancer, it is apparent that it suffers from some limitations in depicting metastases of the osteoblastic type.