Microscopic Extracapsular Extension in Sentinel Nodes
Is Axillary Node Dissection Obligatory?
Whether you follow the dictates of ACOSOG Z0011 using sentinel lymph node biopsy alone or AMAROS using sentinel node biopsy and axillary radiation, omitting axillary lymph node dissection (ALND) for limited disease in sentinel nodes has become customary practice. How to proceed when extranodal extension is present is more controversial. In the past, based on a poor prognosis for these patients, axillary radiation has been recommended with extranodal extension in those having complete ALNDs. (Kuske et al. Int J Rad Oncol Biol Physics. 1996;36:277 ). Unfortunately, the risk of microscopic extracapsular extension (mECE) was not examined in either Z0011 or AMAROS. A recent study from Barrio et al. at Memorial Sloan Kettering Cancer Center addresses this issue.
Eight hundred eleven patients with cT1-2N invasive breast cancer and sentinel node metastases had breast-conserving surgery and were managed according to Z0011 criteria. Of these, 685 patients had one to two positive sentinel nodes treated with sentinel node biopsy alone. mECE was identified in 210 of these patients. These patients were further stratified into those having greater than or less than or equal to 2 mm of mECE. Patients with mECE were more likely to receive nodal radiation than those without mECE (39% versus 17%). Patients receiving nodal radiation were also more likely to have larger tumors and have 2 (versus 1) positive sentinel nodes. The group receiving radiation was also more likely to have greater than 2 mm of mECE.
Although there were no isolated axillary lymph node failures observed at 41 months of follow-up, there were 11 nodal recurrences. Two were limited to the supraclavicular and supraclavicular-axillary nodal basins. Four occurred at the same time as an in-breast recurrence. Five occurred at the time of distant failure. The five-year incidence of any nodal failure was 1.6%. The authors noted no difference in nodal failure in patients with 1 to 2 positive sentinel nodes with or without mECE. However, there were differences noted in the size of the mECE. In the 117 patients who had less than or equal to 2 mm of mECE, there were no nodal recurrences. In the 93 patients with mECE , 3 patients had nodal recurrences. Because there were so few total recurrences the authors could not create a statistical comparison of five-year nodal failure rates for greater than or less than 2 mm of mECE.
If one looks at ACOSOG Z0011 and AMAROS, 27% and 33% respectively had additional nodal disease beyond the sentinel nodes. This additional nodal disease occurred despite low recurrence rates in both studies (less than 2%). At the moment, there is little question that macroscopic extranodal extension is a cause for concern and is an indication for axillary radiation. Unfortunately, the two randomized trials mentioned above did not evaluate the risk of mECE. This study from Memorial Sloan-Kettering suggests several things. First is that microscopic extracapsular extension is relatively frequent. In this series, it was identified in 85% of those who had metastases in more than two sentinel lymph nodes. The study also suggests that there was no differences in nodal failure rates between patients with and without mECE in the absence of ALND, as the nodal recurrence rate at five years was only 1.6%.
The question as to whether radiation to the axilla should be given in these cases has not been answered. Thirty-nine percent of patients in this study with mECE received radiation, which was left up to the discretion of the surgeon and radiation oncologist. However, with such a low axillary recurrence rate, it is unlikely that the addition of radiation will improve local recurrence rates. If one were to consider axillary radiotherapy, it would be only in those patients with mECE greater than 2 mm.