PET
Scans Not Effective for Axillary Node Detection in Breast
Cancer
According to a recent article published in 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.
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.
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