The sentinel node is the underarm (axillary) lymph node closest to a breast cancer. During surgery to remove early-stage breast cancer, the sentinel node often is removed and sent to a pathologist for evaluation. Removing just the sentinel node is called sentinel node biopsy or sentinel node dissection.
Sentinel node biopsy may be done even if the sentinel node looks normal and shows no signs of cancer on an ultrasound or x-ray (called clinically negative). Still, the pathologist may find single cancer cells or small groups of cancer cells in a sentinel node that is clinically negative. These single and small groups of cancer cells are called occult metastases. Occult means the metastases are hidden or not easily seen.
A large study (called NSABP B-32) found that women diagnosed with early-stage breast cancer who have occult metastases in a clinically negative sentinel node do almost as well as women without occult metastases.
Some doctors believe that occult metastases (micrometastases) in a clinically negative sentinel node mean a woman needs a more aggressive treatment plan to reduce the risk of recurrence (the cancer coming back) and improve prognosis. A more aggressive treatment plan might include:
- removing other underarm lymph nodes (axillary node dissection)
- radiation therapy to the underarm lymph nodes (axillary irradiation)
- chemotherapy after surgery
- hormonal therapy after surgery
The researchers wanted to know if a more aggressive treatment plan benefited women with occult metastases in the sentinel node. So they compared the prognosis of women with occult metastases to women who didn't have them.
The 3,887 women in the study were randomly split into two equal groups. One group had only sentinel node biopsy and the other group had sentinel node biopsy AND axillary node dissection. After tissue from the sentinel node was analyzed, 15.9% of the women were found to have occult metastases.
Based on follow-up information, the researchers estimated 5-year survival rates for all of the women. They then compared the survival rates of the women with occult metastases to the survival rates of the women who didn't have occult metastases:
- 94.6% of the women with occult metastases compared to 95.8% of the women without occult metastases were projected to be alive 5 years after diagnosis (overall survival rates)
- 86.4% of the women with occult metastases compared to 89.2% of women without occult metastases were projected to be alive with no cancer recurrence 5 years after diagnosis (disease-free survival rates)
- 89.7% of the women with occult metastases compared to 92.5% of women without occult metastases were projected to be alive with no metastatic recurrence (the cancer coming back in a part of the body away from the breast) 5 years after diagnosis (distant disease-free survival rates)
While overall survival, disease-free survival, and distant disease-free survival rates were slightly lower in women with occult metastases, these differences were small. So more aggressive treatment for all women with occult metastases may not be necessary. Still, other studies show that women with occult metastases consistently have worse outcomes.
If you've been diagnosed with early-stage breast cancer and had sentinel lymph node biopsy, it's a good idea to talk to your doctor about the results of the biopsy. If any occult metastases were found, you might want to talk to your doctor about this study and ask if the results apply to your situation. Your doctor may recommend (or may have already done) axillary lymph node dissection. Or your doctor may recommend axillary lymph node radiation. If occult metastases were found and your doctor didn't recommend or do any additional treatment, you may want to ask about the reasoning behind that decision. Together, you and your doctor can develop a treatment plan that makes the most sense for your unique situation.
Visit the Breastcancer.org Lymph Node Removal pages to learn more about sentinel node biopsy.
Editor's note: To make sure that women have the appropriate lymph node surgery, the American Society for Clinical Oncology released guidelines on sentinel lymph node biopsy for people diagnosed with early-stage breast cancer. The guidelines say sentinel lymph node biopsy SHOULD be offered under these circumstances:
- breast cancer in which there is more than one tumor, all of which have formed separately from one another (doctors call these multicentric tumors); these types of breast cancers are rare
- DCIS treated with mastectomy
- women who have previously had breast cancer surgery or axillary lymph node surgery
- women who have been treated before with chemotherapy or another systemic treatment (treatment before surgery is called neoadjuvant treatment)
Sentinel node biopsy SHOULD NOT be offered under these circumstances:
- the cancer is 5 cm or larger or locally advanced (the cancer has spread extensively in the breast or to the nearby lymph nodes)
- the cancer is inflammatory breast cancer
- DCIS treated with lumpectomy
- the woman is pregnant
The guidelines also say:
- Women with negative sentinel node biopsies shouldn’t have axillary node surgery.
- Women with one or two positive sentinel nodes who plan to have lumpectomy plus radiation also don’t need axillary node surgery.
- Women who have one or more positive sentinel nodes and plan to have mastectomy with no radiation should be offered axillary node surgery.