Sentinel Lymph Node Dissection As a Means of Managing Breast Cancer

AORN Journal, Oct, 2000 by Sandra Wienholz, Susan F. Dean

The lymphatic system comprises the spleen, thymus gland, lymph nodes, and lymphatic vessels or channels. In addition to containing important cells of the immune system, this highly-organized system is one of the body's complex filtration systems and is responsible for removing blood-bound contaminants (eg, bacteria, cancer cells) from the lymphatic fluid before returning it to the venous circulation by way of the lymphatic vessels or channels.(1)

Groups of lymph nodes that collect extracellular drainage from a specific area of the body are known as nodal basins. For example, lymphatic fluid from the breast primarily drains into the axillary nodal basin (ie, 80% to 85%), and some fluid drains into the internal mammary drainage area.(2) By definition, within a specific nodal basin, the sentinel lymph nodes are the first to receive lymphatic drainage from tumors (Figure 1).(3)

[Figure 1 ILLUSTRATION OMITTED]

Of all cancers, breast cancer is the second leading cause of death for all women and the leading cause of death for women ages 40 to 55.(4) In 1999, 175,000 new cases of breast cancer were reported, 43,300 of which were diagnosed in situ (ie, noninvasively).(5) Currently, the stage of the disease determines breast cancer treatment. Stage one consists of a primary cancerous lesion under 2 cm in diameter, with no lymph node involvement. Stage two involves a cancerous lesion 2 cm to 5 cm in diameter, but differs from stage one in that cancer cells also are present in axillary lymph nodes.(6) Treatment for both stages consists of lumpectomy or mastectomy and a radical axillary node dissection. In stage one, the radical node dissection primarily is used as a general diagnostic and prognostic indicator. In stage two, the cancer-involved tissue must be removed to prohibit further spread of the disease. In both cases, treatment is extensive, physically and psychologically traumatic for the patient, and may cause debilitating postoperative complications.

A sentinel lymph node dissection, however, is highly selective, precise, and can minimize the stage one patient's trauma by providing treatment options based on specific lymph node findings. If, for example, the sentinel lymph node dissection yields a negative finding, the stage one patient can completely avoid radical lymph node dissection.(7) A positive sentinel lymph node finding in stage one changes the diagnosis and reclassifies the patient as stage two due to cancer involvement outside the primary lesion. The patient then undergoes a radical axillary node dissection.(8) In stage two, sentinel lymph node dissection is a powerful diagnostic means by which pathologic information precisely defines the extent of the metastases and helps confirm the emergent need for subsequent radical lymph node dissection.

NUCLEAR MEDICINE

Lymphatic mapping provides surgeons and pathologists a means to precisely and thoroughly examine sentinel lymph nodes likely to contain micrometastatic disease from primary lesions. Currently, surgeons use two methods to identify sentinel lymph nodes. The first method, known as tagging, requires the injection of a radioisotope that, upon the application of a gamma probe, provides the surgeon an audible map of the lymph nodes and vessels under investigation. The other method uses a blue contrast dye (ie, isosulfan blue 1%) that, when injected into the tumor, creates a visual map of the lymphatic structures by staining them. These methods can be used together or individually (Figure 2).(9) It is not required that radioactive precautions be used with the patient or when handling the patient's body fluids.(10)

[Figure 2 ILLUSTRATION OMITTED]

Administration of the radioisotope may take place in the nuclear medicine department. It also can be done in the OR, but requires equipment that is too large for most OR suites. Additionally, the injection can take up to two hours, and no anesthesia is required for the procedure. For these reasons, it is cost-effective to administer the radioisotope in an area other than the OR.

When the radioisotope injection is performed, the patient's primary tumor site receives a 0.1 to 0.2 mL injection of technetium (ie, the sulfur colloid H2S technetium) to identify the primary tumor. This injection also identifies the lymphatic basins, nodal areas, and respective lymph draining sites that are considered to be at risk for metastases. In addition, the injection also is used to estimate the number of sentinel lymph nodes present, fix their location in relation to other nodes in the lymphatic basin, and determine which lymphatic channels are involved." Lymphatic basins with the highest radioisotope concentrations receive a preliminary skin-surface mark for the surgeon's convenience. The skin marks generally are made with a skin scribe and appear as simple dots or marks that include letters (eg, LAT for a lateral marking) to ensure the marks do not become transferred to another skin surface before surgery. Conventional practice defines a node as "hot" when it emits 10 times the amount of normal background radiation. A patient may have one or more marks representing "hot" nodes.