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What is Sentinel Lymph Node biopsy and how is it conducted?
Sentinel lymph node biopsy is a surgical approach used for identification of specific lymph
nodes that are called sentinel nodes. The world sentinel means “sentry” or “guard”. In
cancer, a sentinel lymph node is referred to as a lymph node that receives lymph from the
cancer in a patient and thus acts as a first site of spread of cancer to lymph nodes.
In cancer management, removal of lymph nodes is commonly a part of cancer surgery.
Lymph nodes in the axilla (armpit) are removed for breast cancer surgery. Removal of all the
axillary lymph nodes is the standard procedure that has been in use for more than a
century. This process however can lead to some problems such as edema of the arm
(lymphedema), weakness and stiffness of shoulder (impaired shoulder function).
It has been noticed in large studies that lymph nodes in axilla may not contain cancer in a
one third to two third of patients (35% to 65%). In such cases, removal of axillary lymph
nodes does not provide benefit to the patient while the side effects of axillary dissection can
still occur.
To reduce the risk of problems related to removal of axillary lymph nodes, we need to
identify patients whose nodes do not contain cancer. Sentinel lymph node biopsy is an
approach that can identify presence or absence of cancer in axillary nodes. With this
approach, axillary dissection can be avoided in patients who do not actually need it and thus
avoid side effects of axillary dissection.
Sentinel lymph node biopsy is recommended for patients in whom lymph nodes in the axilla
are not enlarged on clinical examination. It is conducted using a combination of two
techniques: blue dye and radioisotope. Radioisotope labeled colloid is injected in the breast
a few hours before surgery. Then, scanning is done using a gamma camera to look for
uptake of radioisotope in the nodes. At the time of surgery, special equipment called
handheld gamma probe is used to identify sentinel nodes in the axilla. A special blue dye is
also injected in the breast at the time of surgery and lymph nodes in the axilla are identified
that have taken up the blue dye. Such stained nodes are part of the sentinel lymph node
group. Thus, both dye method and radioisotope method are combined to get the highest
accuracy rates for sentinel node identification. The sentinel nodes that have been identified
are sent to the pathologist for immediate assessment using “frozen section” testing. If there
is cancer in these nodes, remaining nodes from the axilla are removed. Otherwise,
remaining nodes are not removed.
Advantages & Disadvantages
Main advantage is avoidance of axillary dissection when it is not necessary. Disadvantages
can be described in terms of the need for specialized infrastructure and expertise. Such
infrastructure and expertise is available at specialized centers only.
The blue dye also causes temporary discoloration of breast skin, urine and stools. This
vanishes from urine and stools fairly quickly but breast skin may take several days to come
back to normal colour. There is also a very small risk (less than 1%) of allergic reaction due
to the blue dye. In some patients, it is not possible to identify the sentinel nodes. In this
scenario, the surgeon needs to proceed with axillary node dissection.
Sentinel node biopsy is a helpful option as it leads to quicker recovery and reduces hospital
stay. The patient does not need to carry a drain which is needed after axillary node
dissection. The most important advantage is significantly reduced risk of lymphedema,
better movements of shoulder and less discomfort in the arm.
Blue stained lymph node in the axilla
Hand Held Gamma Probe System
Injection of blue dyebeing carried out
Blue stained sentinel node and blue lymphatic channel
.