Case of the Month—January 2004

Breast Cancer

History and Finding
This patient is a 45-year-old female with a history of breast cancer. A follow-up bone scan showed a focus of increased uptake in the left anterior 3rd rib (Figure 1). The patient had no bone pain, but she did have a fall while skiing two months prior to the bone study. A CT of the chest, abdomen, and pelvis were unremarkable. A whole-body FDG PET study was performed a few days after the bone scan, showing multiple foci of increased uptake in the left anterior upper rib, lower T-spine and L-spine, and right ischium, consistent with metastatic lesions (Figure 2).

Figure 1.

Figure 2.

Follow–up
The patient received chemotherapy, and a repeat bone scan was performed five months later (Figure 3). This follow-up bone scan demonstrated multiple areas of bone uptake almost identical to the pattern of FDG uptake five months before. However, a repeat FDG PET scan at the same time demonstrated complete resolution of the abnormalities (Figure 4).

Figure 3.

Figure 4.

How Did Pet Help?
PET confirmed the suspicion of metastasis as seen from the first bone scan, and PET identified more lesions than the bone study did. Moreover, PET proved to be more useful for monitoring the response to therapy (see discussion below).

Discussion
It has been reported that PET is more accurate than a bone scan for determining lytic metastasis and bone marrow involvement, while bone scan is more sensitive for osteoblastic lesions (1). In general, PET detects metastatic bone lesions from breast cancer earlier than a bone scan does—as proved to be true in this case. In terms of monitoring therapy response, if the patient responds to chemotherapy, a period of increased bone uptake occurs due to the healing process. This is why we see increased bone uptake on the second bone scan. The increase is referred to as a “flare” phenomenon, which should not be confused with progression of the disease. PET is clearly superior to the bone scan in monitoring therapy response.

1. Cook, G.J., et al, “Detection of bone metasteses in breast cancer by 18F-FDG: differing metabolic activity in osteoblastic and osteolytic lesions.” J. Clinical Oncology, 1998, 16:3375-3379.

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