Imaging in breast cancer: Single-photon computed tomography and positron-emission tomography

Abstract

Although mammography remains a key imaging method for the early detection and screening of breast cancer, the overall accuracy of this test remains low. Several radiopharmaceuticals have been proposed as adjunct imaging methods to characterize breast masses by single-photon-emission computed tomography (SPECT) and positron-emission tomography (PET). Useful in characterizing indeterminate palpable masses and in the detection of axillary metastases, these techniques are insufficiently sensitive to detect subcentimetric tumor deposits. Their role in staging nodal involvement of the axillary areas therefore currently remains limited. Several enzymes and receptors have been targeted for imaging breast cancers with PET. [18F]fluorodeoxyglucose is particularly useful in the detection and staging of recurrent breast cancer and in assessing the response to chemotherapy. Several other ligands targeting proliferative activity, protein synthesis, and hormone and cell-membrane receptors may complement this approach by providing unique information about biological characteristics of breast cancer across primary and metastatic tumor sites.

Figure 1

^99mTc-methoxyisobutylisonitrile mammoscintigraphy showing a typical case of breast cancer in the external upper quadrant of the left breast. Panel (a) shows the anterior planar images. Lateral images obtained in the prone position (b) are obtained to improve the detection of smaller breast lesions

Figure 2

[¹⁸F]Fluorodeoxyglucose (¹⁸F-FDG) (a) and 16α-[¹⁸F]fluoro-17β-estradiol (¹⁸F-FES) (b) positron-emission tomography (PET) studies obtained in a patient with newly diagnosed metastatic recurrent breast cancer in the bones. The bone metastases are readily seen in both studies. Whereas ¹⁸F-FDG-PET images provide information about the metabolic activity of the metastases, ¹⁸F-FES images can demonstrate that the recurrent lesions still express high levels of estrogen receptors.