More considerations on the sentinel lymph node biopsy

The sentinel lymph node biopsy is basically a staging technique for invasive cancer, and also provides useful information to guide subsequent therapies. However, it should be noted that not all clinics practice nor recommend the technique. It is the sort of procedure that may be called for in unique situations.

The concept

The basic concept is that the sentinel lymph node is the first to receive lymphatic drainage, and in theory, the first lymph node into which a malignant tumor will metastize. Therefore, a negative status for the sentinel lymph node can just about guartantee that the other nodes are also clear. This is a very good thing, because axillary dissection ( either for biopsy study or removal of potentially malignant axillary ( ie around the armpit ) nodes can result in many complications such as seroma, lymphedema, arm paresthesia, and pain. Furthermore, any disruption in the normal lymphatic flow can (counter/impare/diminish.... need a good word here for 'being counter-productive') positive influences from previous interventions such as breast surgery or radiation therapy.

find references 1 8 and 9 and 13 on the reference page, in the body of the CD

The techniques

The SLN technique involves the injection into the breast area of two different substances: a low radioactive colloid ( usually technetium sulfur ), and a blue dye agent. With the dye, the Sentinel lymph node is stained with the blue color , or found in association with a blue-stained lymphatic channel. With the radio-labelled technetium the identification of the SLN is a little more complicated- it is found as a cross referencing of a number of different indicators. The pathologist will look for any node with 'ex-vivo' counts of greater than 3 to 4 times the normal axillary basin count. ( Aside, 'ex vivo' means the procedure is happening 'outside of an organism', so this means that a sample of blood is taken from the patient, combined with the dye or colloid, and injected back into the patient. The injected substance is then taken up by the lymphatic system and the patient is then scanned to track the behaviour of the dye and radioactive particles) Or, one looks for any node with an ex-vivo count ten times higher than for a non-sentinel mode. Or, one identifies any node with an ex-vivo 10 times greater than the background count, or any radioactive 'hot spot' with counts more than 25 to 30 times higher second ex-vivo. ( Second ex-vivo means a second sample is extracted, combined with fluid, returned to the body, and compared with the orignal base-line readings)

It will take at least 40-60 minutes for the re-injected technetium sulphur colloid to migrate to the sentinel lymph nodes. Some protocols even recommend up to 4 hours between injection and subsequent mapping.The blue dye ( usually isofulfan) however, is very rapidly taken up by the lymphatic system and must be injected less than 10 minutes before the anticipated surgical extraction. Injection sites are typically 'intra or peritumoral'(meaning within or 'within the outer skin' of the tumor), subdermal above the tumor ( below the skin but above the tumor), or given in the subareolar region ( beneath the nipple). After the injection the area is usually massaged by hand for a few minutes to stimulate blood and lymphatic flow. The practice of using these procedures to locate the sentinel lymph node and to trace the movement of lymphatic flow, is called 'lymphoscintigraphy'.

Sensitivity and false negatives

The average sensitivity of the SLN biopsy is about 90% with a false negative rate of about 10%, but this rate is thought to be decreasing as surgeons and pathologists gain more experience with the technique. Usually a surgeon will remove 1 to 3 Sentinel lymph nodes. False negatives are generally the result of not finding a sentinel lymph node or the absence of a sentinel lymph node, metasitasis of the tumor to some area besides the axillar region, or because the lymphatic channels have already been corrupted by the tumor, and/or tumor metastasis to axillary lymph nodes has already occurred. In older patients, a false negative assessment might also be attributed to an excessive amount of fatty tissue within the lymphatic channels which impares the absorption of the investigative fluids.

Other considerations

If axillary adenopathy is clinically palpable, then a sentinel lymph node biopsy should absolutely NOT be performed.(axillary adenopathy means simply 'large or swollen' axillary lymph nodes). The general consensus of opinion is that once lymph node metastases are confirmed in the axillary nodes, they should be surgically removed, immediately. The SLN biopsy is redundant and useless by that point.

Note, the SLN staging technique is not generally used if the presenting diagnosis is DCIS, because the risk of lymph node metastasis is thought to be very low.

reference number 10 for the above.

Back to breast cancer staging list.