Breast cancer is the leading cause of cancer among women in the United States, and the second leading cause of cancer-related mortality. The long-term survival of patients with breast cancer depends critically on the stage at which the disease is first identified. The 5-year survival rate is approximately 99% among patients who are diagnosed while the cancer is still confined entirely to the breast but decreases to less than 25% for patients who are diagnosed with distant metastases. Mammography is widely used in the screening and diagnosis of patients with breast cancer, but is associated with a high false-positive rate and is less effective for identifying cancer in some patient populations (eg, younger women or others with dense breast tissue). Molecular breast imaging is the use of nuclear medicine and other techniques to noninvasively visualize, characterize, and quantify biological processes in living patients. Molecular imaging techniques may make it possible to visualize breast cancer at earlier stages of disease before the appearance of structural breast lesions that are evident on routine mammograms or magnetic resonance imaging (MRI).
Molecular imaging also provides several new tools to individualize treatment selection and to monitor the effects of treatment. Radionuclide imaging approaches use biological probes that are labeled with radioactive tracers. Patients undergoing scintimammography or single-photon emission tomography (SPECT) receive an injection of the gamma emitter 99mTc-sestamimibi (MIBI), which is taken up to a greater degree by cancer cells than by surrounding healthy tissues. Imaging of the breast with a gamma camera reveals sites of elevated MIBI uptake. Alternatively, MIBI imaging may be performed using a high-resolution, small field-of-view gamma camera that has been developed specifically for breast imaging. Positron emission tomography (PET) scanning relies on a different radioactive tracer, 18F-fluourdeoxyglucose (FDG), to identify regions of heightened metabolic activity. Whole-body PET has been primarily been used to identify lymph node involvement or metastatic disease in patients with breast cancer, whereas dedicated devices have recently been introduced that provide higher-resolution PET imaging of the breast (positron emission mammography [PEM]). Many other radionuclide markers are being developed to identify other targets that are important in cancer research and treatment, including cell-surface receptors for hormones or growth factors that contribute to tumor development. MRI techniques that have been used to image biological processes in patients with breast cancer include magnetic resonance spectroscopy and diffusion-weighted MRI. Finally, many other investigational approaches are also being examined in clinical studies, including biological contrast-enhanced ultrasound, calculation of tissue hemoglobin content by infrared laser, and dynamic contrast MRI.
After reading this article, the participant should be able to:
- RECALL some of the limitations of conventional mammography for breast evaluation and the rationale for molecular imaging.
- EXPLAIN commonly used radionuclide methods of breast cancer assessment and describe their mechanisms of action and primary clinical applications.
- NAME the role of magnetic resonance imaging (MRI) methods in molecular breast imaging.
- LIST investigational techniques that are in development for molecular breast imaging, and briefly describe their proposed mechanisms of action.