Positron Emission Tomography and Breast Cancer staging
PET scans are sometimes used in breast cancer diagnosis and follow-up. Positron Emission Tomography has a very high sensitivity rate, and may be useful in differentiating breast cancer from other benign lesions, especially for lesions 7 mm or greater. On the whole PET imaging is not used for initial screening purposes, and has relatively small role with respect to primary breast cancer. It is often used as a complement to conventional imaging in improving the characterization of breast lesions and may show multifocal involvement.
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Positron Emission Tomography (PET) most commonly uses radiopharmaceutical 18F-fluorodeoxyglucose (labelled with “F18 in the FDG molecule) which is injected intra-venous. The F18 emits positrons in such a way, that a 3 dimensional image can be created. With a dedicated PET camera, it is possible to view the distribution of FDG and to identify tumors. The FDG molecule is a form of non-metabolized glucose that is absorbed by cells proportionally to glucose metabolism.
Malignant cells typically have and increased glycolytic rate, therefore making it possible to differentiate cancer cells from benign tissue. New PET tracers, such as radio-labeled thymidine, are being developed that will monitor tumor growth with greater specificity, detailing elements such as early tumor response and recurrence after irradiation.
Below is a PET scan reconstructed in 3-D, which reveals a lesion on the left breast, multiple liver metastasis, a sacra bone metastasis, axillary and supra-clavicular adenopathies, and other tumors behind the bladder.
PET scanning perhaps the only non-invasive imaging procedure that can detect tumors in the breast, lymph nodes, liver, lung, and bone and bone marrow with reasonable accuracy and high sensitivity. It may be a valuable tool in staging and management breast cancer, but in spite of its high sensitivity, it is often difficult to differentiate the different elements of the scan.
PET imaging does not detect microscopic metastatic disease, and cannot reliably determine the number of involved lymph nodes. Commonly found false-positive results with PET scans are caused by infectious or inflammatory lesions, which may include mastitis, hemorrhagic inflammation after biopsy or surgery, low-grade malignancy (tubular, lobular), and non invasive carcinoma (in situ).
So, while FDG-PET may be more sensitive perhaps than conventional imaging in the detection of metastatic or recurrent breast cancer, the overall impact of the increased sensitivity of PET scans used for staging in terms of patient care and overall outcome has really not been demonstrated.
For further reading, I suggest you visit this page to know more information about breast cancer screening using PET scans.
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