Abstract PD8-05: POSNOC - Positive sentinel node: Adjuvant therapy alone versus adjuvant therapy plus clearance or axillary radiotherapy

Abstract

Abstract Background: Role of additional axillary treatment (AxT) (axillary lymph node dissection (ALND) or axillary radiotherapy (ART)) in women with ≤2 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, NCIC 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 tumours. A post-Z11 survey shows that most US radiation 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, microscopic extranodal invasion and sentinel node biopsy (SNB) before neoadjuvant chemotherapy. Methods: Primary objective is to assess whether for women with ≤2 macrometastases at SNB, systemic therapy alone is non-inferior to systemic therapy plus AxT in terms of axillary recurrence at 5 years. Secondary objectives are arm morbidity assessed by LBCQ and QuickDASH questionnaires; QoL assessed by FACT-B+4 questionnaire; anxiety assessed by STAI; loco-regional recurrence; distant metastasis; time to axillary recurrence; axillary recurrence-free survival; DFS; OS; contralateral breast cancer; non-breast malignancy; and economic evaluation. Eligibility criteria include: ≥18 y, uni or multifocal invasive cancer, T1/T2, 1 or 2 macrometastases, with or without extranodal invasion. Target sample size is 1900 with a projected drop-out and non-compliance with treatment allocation rate of 10%. Primary analysis will be per protocol. The following pre-specified subgroup analyses shall be performed: number of macrometastases (1, 2), age (<50, ≥50), breast surgery (mastectomy, BCS), ER (positive, negative), tumour grade (1 or 2, 3), SN assessment technique (OSNA, non-OSNA), extranodal invasion (present, absent). POSNOC opened to recruitment in July 2014. To date 1100 women have been recruited at 82 sites in the UK and 18 sites in Australia and New Zealand. Clinicaltrials.gov NCT02401685. Citation Format: Goyal A, Mann B, Thompson AM. POSNOC - Positive sentinel node: Adjuvant therapy alone versus adjuvant therapy plus clearance or axillary radiotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD8-05.