POSNOC: Positive Sentinel Node—Adjuvant therapy alone versus adjuvant therapy plus clearance or axillary radiotherapy.

TPS600Background: Role of additional axillary treatment (AxT) (axillary lymph node dissection (ALND) or axillary radiotherapy (ART)) in women with macrometastases and undergoing systemic therapy remains unclear. Z11 included both micro and macrometastases (around 40% micrometastases) and showed that ALND may be omitted in women with ≤2 positive nodes undergoing breast conserving surgery (BCS) and receiving whole breast RT. Paradoxically, MA20, demonstrated improved DFS following the addition of regional RT. 51.8% (949/1832) had 1 or 2 positive nodes. 98.9% (1812/1832) had T1/T2 tumors. A post Z11 survey shows that most US oncologists treat the undissected axilla in women with macrometastases with ART rather than omitting AxT. Therefore, a confirmatory study is needed to clarify the role of additional AxT in women with ≤2 macrometastases undergoing BCS and other subgroups that were not included in Z11 e.g. mastectomy, extranodal invasion and sentinel node biopsy (SNB) before NACT. Methods: Primary objectiv...