Sentinel node biopsy explained
One of the most recent advances in the diagnosis of the spread of breast cancer is the use of a sentinel node biopsy. So what does it involve and what has it replaced?
The sentinel nodes are the nodes, usually in the axilla (under the arm) to which breast cancer cells are most likely to spread to first. Generally they are located closest to the breast tissue. A sentinel node biopsy involves removing far fewer nodes than a complete axillary clearance – which was the traditional way of establishing if the cancer had spread to the lymphatic system.
The term ‘biopsy’ in this context can sometimes be misinterpreted, as it differs from a traditional ‘biopsy’, in that it involves the removal of several lymph nodes in their entirety (rather than just a small tissue sample from each) to send to pathology for testing.
According to Specialist Breast and Oncoplastic Surgeon, Dr Jane O'Brien, the presence or absence of any cancer cells in the lymph nodes is a very important prognostic tool, and also guides the post-operative treatment recommendations for breast cancer, including chemotherapy and radiotherapy.
“We have always examined the lymph nodes to check the spread of the cancer through the lymphatic system. In a sentinel node biopsy, we are simply cherry picking a much smaller number of those nodes which are the most likely to be involved.
“If we test the sentinel lymph nodes, we have an indication of whether there has been any cancer spread via lymphatic system, and a complete removal (sometimes called clearance or dissection) of all of the remaining nodes will not be required if the sentinel nodes are cancer free,” Jane says.
So what does a sentinel node biopsy involve?
“Firstly, it is important to note that we usually do a sentinel node biopsy at the same time as the surgery to remove the breast tumour,” Jane says.
“Before the operation, the patient has some radioactive material injected into the affected breast – generally on the day of surgery or the previous day if required.
“Then during surgery the surgeon injects some blue dye into the breast. Those lymph nodes which are “blue”, or are “radioactive” when probed intraoperatively with a handheld radiation counter, are the so called ‘sentinel nodes’,” she says.
The surgeon removes all the blue and radioactive nodes, and sends them for pathology to determine whether there is any cancer present in these nodes.
Jane says the number of sentinel nodes that are removed can vary from person to person. “Generally it is under five, but most commonly perhaps three or four. This compares with an axillary clearance which can remove up to 20 or 30 lymph nodes,” she says.
"When all the lymph nodes are removed simply to determine whether they are involved or not, there is a higher chance of swelling developing, when it may not have even been necessary in the first place," Jane says.
The benefits of a sentinel node biopsy over a complete axillary clearance are that the lymphatic system is less disrupted and the surgery is less invasive. Patients do not usually require a drain in their arms after the sentinel node operation.
Jane says the side effects include blue urine for around 24 hours after the operation, and there is a rare chance of an allergic reaction to the blue dye injection.
“We believe that this is a much better diagnostic tool, where previously we had no other option available but to remove all the lymph nodes. The majority of patients do not require a complete axillary clearance and will therefore have no unnecessary major disruption to the lymphatic system in the arm,” Jane says.
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