Differences in Radiotherapy Coverage in the ACOSOG Z0011/Alliance Trial in Breast Cancer
The ACOSOG Z0011/Alliance trial showed that axillary lymph node dissection provides no benefit over sentinel lymph node biopsy in patients with breast cancer with one or two positive sentinel lymph nodes undergoing lumpectomy, radiotherapy, and systemic therapy. In an analysis reported in the Journal of Clinical Oncology, Jagsi et al found that although the majority of patients in the trial received protocol-specified radiotherapy, there was variation in radiotherapy coverage of regional nodes in a substantial proportion.
The ACOSOG Z0011 protocol specified that patients receive whole-breast radiotherapy using standard tangential fields and that a third field of directed nodal treatment not be used. However, the study radiation oncologists could not be blinded to the treatment assignment to axillary lymph node dissection vs sentinel lymph node dissection and had discretion over the extent of the axillary contents included in tangential radiotherapy fields. It has thus been speculated that they may have systematically treated patients in the sentinel lymph node dissection group with high tangents to include axillary level I/II components and used this approach less frequently in the axillary lymph node dissection group.
Use of Whole-Breast Radiotherapy and High Tangents
The analysis involved case report forms completed 18 months after enrollment in the trial. All available detailed radiotherapy records from 2012 to 2013 were collected for central review. Among 605 patients with completed case report forms, 540 (89.3%) received whole-breast radiotherapy and 89 (14.7%) also received radiotherapy to the supraclavicular region.
Among 228 patients with detailed radiotherapy records, 185 (81.1%) received tangent-only treatment. Among 142 with sufficient records to assess tangent height, high tangents (cranial tangent border ≤ 2 cm from the humeral head) were used in 33 (50%) of 66 patients randomly assigned to axillary lymph node dissection and in 40 (52.6%) of 76 randomly assigned to sentinel lymph node dissection. Treatment group was not associated with use of high-tangent radiotherapy on either univariate or multivariate analysis.
Use of Directed Nodal Radiotherapy
Of the 228 patients with detailed records, 43 (18.9%) received directed regional nodal radiotherapy using at least three fields, including 22 patients in the axillary lymph node dissection group and 21 in the sentinel lymph node dissection group. Patients who received directed nodal radiotherapy had greater nodal involvement (P < .001) than those who did not.
Of three patients with zero nodes involved, all were in the sentinel lymph node dissection group and one received directed nodal radiotherapy. Of the 140 patients with one node involved, 13 (9.3%) received directed nodal radiotherapy, including 4 (7.3%) of 55 in the axillary lymph node dissection group and 9 (10.6%) of 85 in the sentinel lymph node dissection group. Of 44 patients with two nodes involved, 9 (20.5%) received directed nodal radiotherapy, including 3 (15.8%) of 19 in the axillary lymph node dissection group and 6 (24.0%) of 25 in the sentinel lymph node dissection group.
Of 9 patients with three nodes involved, 5 (55.6%) received directed nodal radiotherapy, including 2 (33.3%) of 6 in the axillary lymph node dissection group and 3 (100%) of 3 in the sentinel lymph node dissection group. Of 16 patients with at least four nodes involved, 13 (81.3%) received directed nodal radiotherapy, including 11 (78.6%) of 14 patients in the axillary lymph node dissection group and 2 (100%) of 2 in the sentinel lymph node dissection group.
Overall, there was no significant difference between treatment groups in the use of protocol-prohibited nodal fields.
The investigators concluded: “Most patients treated in Z0011 received tangential [radiotherapy] alone, and some received no [radiotherapy] at all. Some patients received directed nodal irradiation via a third field. Further research is necessary to determine the optimal [radiotherapy] approach in patients with low-volume axillary disease treated with [sentinel lymph node dissection] alone.”
Reshma Jagsi, MD, DPhil, of University of Michigan, is the corresponding author for the Journal of Clinical Oncology article.
The study was supported by National Cancer Institute grants. Dr. Jagsi reported a consulting or advisory role with Eviti and research funding from AbbVie.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
