The Breast Journal, positron emission tomography (PET) scans are not accurate enough to aid in nodal staging of breast cancer.

In breast cancer, a common site of cancer spread is to the lymph nodes under the arm (axillary nodes) of the affected breast. One important variable in cancer staging (the determination of the extent of spread of cancer) in patients with early breast cancer is determining the number of axillary lymph nodes to which the cancer may have spread. Accurate staging is important as the stage dictates treatment options for a patient. Detection of axillary cancer spread may be done through the surgical removal of a large number of axillary lymph nodes (axillary lymph node dissection) which are examined through laboratory processes to detect the existence of cancer cells, or through a sentinel lymph node biopsy, which utilizes the detection of the axillary lymph node that has the highest probability of cancer spread for evaluation of cancer spread. In order to reduce the side effects that may be caused by these procedures, researchers have been evaluating non-invasive methods, such as scans, in which to detect cancer spread to axillary lymph nodes.

Positron emission tomography scans are commonly used in the detection and staging of various cancers. PET scans are able to distinguish between dead tissue and active cancer cells by exploiting a biological characteristic of rapidly dividing cancer cells – the metabolism of sugar. A solution containing a type of sugar attached to a radioactive compound is injected into the vein of a patient undergoing a PET scan. Cancer cells tend to take up more sugar than normal cells, so the solution becomes concentrated in the cancer. The attached radioactive compound emits a form of radiation that can be detected by the PET scanner. The scanner then forms a picture that allows the physician to see the location of small amounts of cancer cells if they exist. However, PET scans have limitations in their accuracy in various types of cancers and researchers continue to evaluate their efficacy as a staging or detection tool, or as a measure to evaluate responses to therapy.

Researchers recently evaluated the effectiveness of PET scans for the accuracy in detecting cancer spread to axillary lymph nodes in patients with early breast cancer. This trial included 24 patients who underwent a PET scan followed by a sentinel node biopsy, as well as an axillary lymph node dissection. Ten patients had cancer spread to their axillary lymph nodes as determined by their biopsies. PET scans only detected 2 (20%) of these patients as having axillary spread. These authors concluded that the use of PET scans for the staging of breast cancer involving the axillary nodes is not accurate enough to be used in the clinical setting for that purpose.

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Reference: Daniel Fink, Hans C. Steinert, Mathias K. Fehr, et al. Axillary staging using positrom emission tomography in breast cancer patients qualifying for sentinel lymph node biopsy.

The Breast Journal. 2004;10:89-93.