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Sentinel Node Biopsy Update
A sentinel node biopsy is a technique that may help limit the number of axillary dissection that are performed for breast cancer. Since the extent of an axillary dissection is related to the incidence of lymphedema, the use of sentinel node biopsies instead of an axillary dissectioin may reduce the risk of developing lymphedema. I have previously discussed the issue of sentinel node biopsies (Sentinel Node Biospy, Sentinel Lymph Node Biopsy: Stud
y Update, Follow up on the sentinel lymph node biopsy).
A question that has not been fully answered is whether a limited technique such as sentinel node mapping is as accurate as an axillary dissection. In a recent study, 343 women underwent both sentinel node mapping and an axillary dissection. 125 of the 343 women had a positive sentinel node and 218 had negative sentinel nodes after pathological analysis. Of the 125 with involved sentinel nodes, almost half were found to have additional lymph nodes involved with cancer when the axillary dissection was perfor
med. Therefore, a positive sentinel node suggests that the likelihood of finding additional involved lymph nodes is about 50% and that further studies including an axillary dissection may be needed to remove all detectable cancer.
Among the 218 women where the sentinel lymph node was negative, 15 were subsequently found to have involved lymph nodes when the axillary dissection was performed. Taking a look at the group as a whole, of the 343 women who were studied, 125 had lymph nodes correctly identified by sentinel node biopsy and 15 had lymph nodes that were missed. Therefore, 140 (125 by sentinel node and 15 by axillary dissection) women had positive lymph nodes and 15 of the 140, approximately 10%, were missed by the sentinel no
Efforts are being made to further improve on the results of sentinel node biopsies. To perform the sentinel node biopsy a blue dye or a radiographic tracer are placed under the skin. These tracers drain to the regional lymph node which is then identified and surgically removed for inspection by the pathologist. These two techniques were compared in a study of 814 women. The dye method correctly identified the sentinel node in 72% of the cases and the radiographic tracer correctly identified the sentinel no
de in 79% of the cases. The best results were obtained with a combination of the two methods. When both techniques were used together the detection rate increased to 90%. As has been found in most studies, the predictive value of the tests were highest in the hands of experienced physicians.
In my opinion, the sentinel node biopsy is a great step forward. Using this test we hope to significantly reduce the number of unnecessary axillary dissections that are preformed each year and as a result we hope that the number of women who develop lymphedema will be dramatically lower in the future. Further work to improve this technique is underway. However, as is always the case in medicine, there are limitations to any technique. In about 10% of cases the cancer cells do not go to the sentinel node. I
f this happens, the sentinel node biopsy will show no evidence of cancer and lymph nodes involved with cancer will be missed. It is also important to recognize that not all patients are good candidates for sentinel node biopsies. The sentinel node biopsy is most effective in women who have only one tumor mass in the breast that is less that about an inch in size. If there are several tumor masses or if the tumor mass is large, the sentinel node biopsy is much less reliable. In addition, if lymph nodes can
be detected by either physical exam or by ultrasound, then the probability of involvement multiple lymph nodes with cancer is high. Finally, sentinel node biopsy is more reliable among women who have not had prior surgery. Prior surgeries including lumpectomies can alter the lymphatic flow and, as a result, reduce the reliability of sentinel node mapping.
In a related news story, the survival rates among women who have recurrent breast cancer were compared for the last 25 years. 25 years ago if a woman underwent treatment for cancer and then had the cancer reappear, the expected survival was a little more than 1 year and only 10% of women were still alive 5 years later. Over the last 25 years new treatments have been introduced including better chemotherapeutic and hormonal drugs. In addition, better techniques for early detection have been developed and im
plemented. As a result, a woman today whose cancer comes back after the initial treatment, has an average expected survival of nearly 4 years. Over 40% of these women live longer than 5 years. We have made a tremendous amount of progress over the last 25 years and we will continue the fight against cancer and lymphedema. I expect that we will see the rates for lymphedema decrease considerably over the next 25 years and several of the necessary tools are available now. Early detection and treatment of breas
t cancer is critical. If most cancers can be detected while they are small, then sentinel node biopsies will be sufficient and most axillary dissections can be avoided. You can help prevent lymphedema by taking steps to catch breast cancer early. Be aware of the warning signs of cancer, perform monthly self-examinations, have regular mammograms and see your doctor regularly.
Tony Reid MD Ph.D