Imaging Bone Metastases in Breast Cancer

doi:10.2214/AJR.05.5143

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Imaging Bone Metastases in Breast Cancer

Ferris M. Hall

Harvard Medical School and Beth Israel Deaconess Medical Center Boston, MA 02215

In the April issue of AJR, Uematsu et al. [1] assessed "the advantagesand disadvantages of different radionuclide imaging techniques (i.e.,¹⁸F-FDG PET and bone scanning) in detecting bone metastases...in the screening and treatment planning of breast cancer patients."These authors found that "FDG PET was less sensitive... in detectingosteoblastic metastases but more sensitive in detecting osteolyticmetastases." This presumably reflects the increased metabolic activityand uptake of the glucose analog in the abundant tumor cellsin lytic metastases, whereas traditional bone scanning agentsare more reflective of osteoblastic activity and blood supply.Hence, less-aggressive sclerotic metastases containing nonmalignantreparative woven bone with an increased number of osteoblastsand fewer tumor cells would be expected to be more sensitiveto traditional bone scanning. Osteoblasts also produce alkaline phosphatase,and people with sclerotic metastases have relatively higher levelsof serum alkaline phosphatase than those with lytic metastases,similar to growing children having higher levels of alkalinephosphatase than adults. Low-grade, well-differentiated tumorsalso are more capable of producing and secreting substancessuch as polypeptides, as in the case of prostate-specific antigen(PSA) in prostate tumors and serotonin in carcinoid tumors.

Metastases are usually classified on the basis of radiographsas lytic, blastic, or mixed, whereas Uematsu et al. [1] usedonly two categories, classifying lesions with any scleroticfoci as blastic. More important, these authors made this classificationon the basis of CT images, which are more sensitive to smallsclerotic foci than are radiographs. I suspect this use of CTis the reason "our series included no patients with osteolytic lesionsonly" [1]. In my experience most bone metastases from breastcancer are initially radiographically lytic. However, becausemetastatic breast cancer is a relatively indolent disease, scleroticor mixed bone metastases are the rule in long-term survivors.I suspect that women who are restaged after treatment will haveless-sensitive ¹⁸F-FDG PET scans of individual lesions whencompared with their pretreatment imaging. This assessment wasnot made by Uematsu et al. [1], and only six of their 15 patientshad any bone metastases.

In summary, aggressive primary or metastatic bone tumors aremore lytic and theoretically should have increased sensitivityfor ^18FFDG PET imaging. On the other hand, less aggressive tumorssuch as breast or prostate cancer or tumors rendered less aggressiveby chemotherapy or radiation are more likely to have scleroticmetastases and be more sensitive to detection by traditionalbone scanning. Unfortunately, biology is never simple, and recent evidencehas questioned many of these traditional assumptions, suggestingthat bone destruction from metastases may reflect osteoclasticstimulation rather than destruction by the tumor itself [2, 3].

References

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References
References

Uematsu T, Yuen S, Yukisawa S, et al. Comparison of FDG PET and SPECT for detection of bone metastases in breast cancer. AJR 2005; 184:1266 -1273[Abstract/Free Full Text]
Roodman GD. Mechanisms of bone metastases. N Engl J Med 2004; 350:1655 -1664[Free Full Text]
Hall FM. Bone metastases. (letter) N Eng J Med 2004; 351:195[Free Full Text]

Reply

Takayoshi Uematsu

Shizuoka Cancer Center Hospital Shizuoka 411-8777, Japan

We agree with the points raised by Dr. Hall. In our study [1],the goal was to see whether the use of traditional bone scanningfor detection of bone metastases in breast cancer is betterthan that of ¹⁸F-FDG PET. Our conclusion is that bone scanningis superior to ¹⁸F-FDG PET in detecting bone metastases in breastcancer. The poorer results in detecting bone metastases with¹⁸F-FDG PET in breast cancer could be explained by the small numberof purely osteolytic metastases in breast cancer. In our study,mixed bone metastases were classified as osteoblastic lesions,and this study showed the low sensitivity of ¹⁸F-FDG PET indetecting osteoblastic and mixed bone metastases when comparedwith traditional bone scanning.

Breast cancer is a heterogeneous disease and some patients,whose survival duration may be a few months, have aggressivedisease. However, many patients with breast cancer have moreindolent disease that is responsive to hormone therapy or chemotherapy.Moreover, except for the low-risk subset that never has bonemetastases, adjuvant hormone and/or chemotherapy is an appropriate considerationin many breast cancer patients. Because adjuvant chemotherapy mightchange purely osteolytic lesions into mixed bone metastases,cases of breast cancer with purely osteolytic metastases onlyare not common, in our opinion.

In conclusion, ¹⁸F-FDG PET is not a powerful tool for detection ofbone metastases in breast cancer. Understanding the advantagesand disadvantages of different isotope imaging techniques, thatis, ¹⁸F-FDG PET and bone scanning in detecting bone metastases,will assist the clinician in breast cancer patient screeningand treatment planning. Routinely performed bone SPECT imagingis practicable and cost-effective and improves the sensitivityof bone scans. We will look forward to follow-up tests becausea larger study population and more outcome data are needed toconfirm our results.