Staging for breast cancer involves the evaluation of the regional lymph nodes. Sentinel lymph node biopsy was developed to allow for assessment of the axillary lymph node status without a formal axillary dissection. The principle of sentinel node identification and removal is that the sentinel node(s) will be affected by regional lymph node tumor spread before the rest of the lymph nodes in that regional nodal basin. The identification, removal, and careful analysis of those lymph nodes can allow for the classification of the spread of the tumor and allow for prognostication. Traditionally, when a sentinel lymph node was positive, that was a trigger for performing a formal axillary dissection and removing all lymph nodes from the axilla. However, more recent evidence suggests that complete axillary dissection is not necessary for certain circumstances, even with a positive sentinel node. This fact is important because axillary dissection is a morbid procedure, with complications including lymphedema, nerve injury, ongoing pain, and lymphangiosarcoma. To safely forego completion axillary dissection with a positive sentinel node, a patient should have a T1 or T2 primary tumor and less than three nodes involved with tumor.
The identification of an axillary sentinel lymph node is typically in the axillary fat pad in the level I or level II lymph nodes of the axilla. These lymph nodes are referred to by anatomists as the pectoral nodes and clavicular nodes. The axillary fat pad lies deep to the fascia superficialis of the axilla and has a different texture than subcutaneous fat. The surgeon divides the superficial fascia during sentinel lymph node biopsy. The clavipectoral fascia lies deep to the pectoralis major muscle and invests the axillary artery and vein, as well as the axillary nerve. Two branches off the axillary artery can be encountered during axillary surgery: the lateral thoracic artery and the thoracodorsal artery. There are two motor nerves of concern in axillary surgery: the long thoracic and the thoracodorsal nerves. Injury to the long thoracic nerve, which provides innervation to the serratus anterior muscle, causes winging of the scapula. Several small sensory nerves traverse the axillary fat pad, including the intercostobrachial nerve. Injury of these nerves causes numbness of the medial upper arm. The surgeon should not encounter the brachial plexus during axillary dissection, provided that dissection is inferior to the axillary vein, which is an important landmark. Dissection superior to the axillary vein does not increase lymph node count for axillary dissection and can cause severe lymphedema and nerve injury.
Sentinel lymph node biopsy is indicated as part of the staging workup of early-stage breast cancers of epithelial origin, such as ductal and lobular carcinomas, since these tumors metastasize to lymph nodes. Sarcomatous tumors of the breast typically metastasize to the lung and do not involve the axillary lymph nodes. For example, cystosarcoma phyllodes tumors are not evaluated with sentinel lymph node biopsy. In patients with invasive ductal and lobular carcinomas, T1 and T2 lesions, merit consideration considered for sentinel lymph node biopsy. The exception to this is if preoperative imaging, either ultrasound, mammogram, or MRI, shows evidence of possible lymph node enlargement. Core needle biopsy of these enlarged nodes is typically performed before lymph node surgery. Some advocate for a complete axillary dissection if two or more axillary nodes are positive for malignancy. Some studies have found preoperative axillary imaging to be unhelpful in patients without palpable lymph nodes. Other studies have found that preoperative ultrasound showing three or more abnormal lymph nodes is a significant predictor of a high axillary nodal burden. The decision about whether or not to obtain preoperative imaging rests with the clinician. PET scan has been used preoperatively in some settings, and evidence suggests that a PET scan showing axillary involvement is a good indication for a complete axillary lymph node dissection, while a negative PET does not rule out lymph node involvement and should trigger sentinel node biopsy. Sentinel lymph node biopsy in patients receiving neoadjuvant chemotherapy presents a particular challenge. Typically, lymph node sampling is carried out before neoadjuvant chemotherapy, as sentinel lymph node biopsy following chemotherapy is not reliable. The decision about whether or not to do a sentinel node biopsy at the time of prophylactic mastectomy is controversial. Occult malignancy is present in 7% to 10% of prophylactic mastectomy specimens. Both preoperative MRI and SLNB have undergone evaluation for prophylactic mastectomy. MRI is less accurate and more costly than SLNB in this setting. Many clinicians will offer SLNB to high-risk prophylactic mastectomy patients since the opportunity for SLNB is gone after a mastectomy. Sentinel lymph node biopsy for multicentric breast cancer has demonstrated effectiveness in patients with clinically negative axillae, with a very low rate of axillary recurrence when performing axillary node dissection for a positive sentinel lymph node.
Sentinel node biopsy is not indicated in patients with bulky axillary disease or with large tumors of the breast, where extensive axillary involvement is suspected. Some evidence exists that preoperative lymph node core needle biopsy can be offered to patients ahead of surgery. If that is positive, their likelihood of needing completion axillary dissection is higher due to increased nodal burden. The role of sentinel lymph node biopsy in patients undergoing neoadjuvant chemotherapy is somewhat controversial. Most patients will undergo lymph node biopsy before neoadjuvant chemotherapy since sentinel node biopsy following neoadjuvant chemotherapy has a high false-negative rate (over10%).
To perform this procedure, an operative suite equipped with surgical instrumentation, surgical support personnel, and anesthesia is necessary. A handheld gamma probe is necessary for axillary sentinel lymph node biopsy if using radiotracer. Many models of gamma probe are available. Typical units will allow for a count as well as average radiation readings. The node is treated as radioactive, and managing the potential residual radiation in the operating room is done per hospital policy.
General surgeons, oncologic surgeons, and breast surgeons are capable of performing sentinel lymph node biopsies for breast cancer. Sentinel lymph biopsy is typically performed under general anesthesia or deep sedation. If using a radiotracer, placement generally is by a radiologist into or adjacent to the tumor bed, or in the subareolar tissue, before the procedure.
Informed consent is necessary, and a careful and clear conversation had with the patient about the indications for completion axillary dissection. Typically, completion axillary dissection is not done at the time of sentinel node biopsy. However, in cases in which pathology is available to give results of a frozen section during the operation, a completion dissection can be performed. If using a radiotracer, the patient should be scheduled for injection by radiology early on the day of the procedure. Lymphoscintigraphy is optional but can be helpful if there is any concern that the sentinel node may be located elsewhere, like the internal mammary nodes. Internal mammary nodes are not retrieved. Internal mammary node involvement can be more common in tumors of the lower inner quadrant of the breast.
The patient’s skin is prepared for surgery in standard fashion. The axillary node biopsy is done prior to any breast surgery planned for that day. If blue dye will be in use in addition to a radiotracer, it is injected either near the tumor bed without radiographic localization or under the areola. This is done just before the start of the procedure because the blue dye is a much smaller molecule than the radiotracer, and it moves faster in the lymph system. Breast massage helps facilitate the movement of the blue dye. If radiotracer has been injected prior, the gamma probe is an option to plan the site for incision, which is usually lateral to the pectoralis major muscle. The gamma probe then guides dissection through the subcutaneous fat and into the axillary fat pad to the node that registers on the gamma probe. When also using blue dye, this node is usually also blue. Care should be taken not to angle the gamma probe toward the site of injection on the breast as this can falsely elevate the amount of radioactivity picked up by the probe and can cause dissection to be misguided. Once the node is identified and retrieved, a reading from the node off of the field is taken, and a reading of background is taken within the wound. If the background reading is high, then the search for an additional node should continue. After obtaining hemostasis, the wound is closed per surgeon preference. Frozen section of the lymph node is not necessary if completion axillary dissection is not planned based on the result.
If using only blue dye, the incision is at the lateral border of the pectoralis muscle, and the blue node can usually be located by direct visualization only.
Sentinel lymph node biopsy is a less morbid procedure than formal axillary dissection. Risks of the procedure include bleeding, infection, nerve injury, lymphedema, and the need for additional surgery in the case of extensive nodal involvement or recurrent axillary disease. It is considered a low-risk procedure.
Sentinel node biopsy for breast cancer has revolutionized breast cancer care. It has spared countless women the morbidity associated with axillary dissection. A critical study was carried out by the ACOSOG in 2010, which demonstrated excellent regional control and suggested no change in survival in early-stage breast cancer patients treated with SLN biopsy compared to patients treated with axillary dissection. The study randomized early-stage breast cancer patients (T1 and T2 lesions) to receive either sentinel node biopsy or complete axillary dissection. All of the patients received adjuvant chemotherapy. Although there are limitations to that study, its results have found broad acceptance, and axillary dissection is no longer an option in many cases of a positive sentinel node. Follow-up studies have indicated that, indeed, 10-year overall survival is not affected by favoring sentinel lymph node biopsy over axillary lymph node dissection.
On the day of surgery, the patient comes into contact with many specialties, and even more, are involved during their cancer care. All caregivers should be aware of their other colleagues administering care, and should communicate with them frequently, functioning as an interprofessional team. Following surgery, a medical oncologist or surgeon typically spearheads treatment plans, ideally with the help of an interprofessional tumor board. Tumor board involves surgeons, medical and radiation oncologists, radiologists, pathologists, nursing staff, and care coordinators so that all members of the team are aware of the treatment options and plan. Nursing care will be crucial in the postoperative setting, administering medication, and closely monitoring patient status so they can inform the clinicians of any status changes. If the patient has any issues with arm mobility after surgery, physical therapy can be employed. A lymphedema clinic is useful if the patient develops lymphedema, though this is rare with just a sentinel lymph node biopsy. Finally, cancer support groups can be of great benefit to patients. The interprofessional team approach, as outlined above, will yield the best results in these cases. [Level 5]
Standard nursing care for the surgical patient applies to this procedure. The staff should follow standard inpatient nursing protocols.
Nurses should be aware that when using isosulfan blue or methylene blue to identify the sentinel node, it can temporarily change the patient's skin tone and will also temporarily cause the patient's urine to be green.
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