Abstract P3-03-14: Clinical utility of one-step nucleic acid amplification (OSNA) in axillary surgery after neoadjuvant chemotherapy (NAC)
Authors: Muscara F , Christaki G , Richardson C , O'Connell R , Padmanabhan P , Warwick J , Lee Y , Smith I , Nerurkar A , Osin P , Krupa K , Rusby J , Roche N , Gui G , MacNeil F , Barry P 
Published: May 2019

Abstract
Introduction
NAC has been used for downsizing of the tumour in breast and axilla to allow more conservative surgery. In the NAC setting, intraoperative assessment of sentinel lymph node(s) (SLN) is still considered necessary1. Current awareness of the prognostic value for axillary nodal down-staging has renewed interest in analysis of SLN post-NAC.
In this study we want to examine the clinical utility of OSNA (based on CK19 mRNA detection) as a method of intra-operative analysis of SLN to assist real-time decision-making for axillary surgery post-NAC in early breast cancer (EBC).
Methods
Retrospective analysis of prospective data on 399 consecutive patients with EBC who received NAC followed by breast surgery with SLN biopsy (408 axillae) and assessment by OSNA, from September 2011 to January 2018 at the Royal Marsden Hospital (UK). OSNA readouts from the Sysmex RD-100i were collected separate to and blinded from clinico-pathological data. A negative or benign pre-treatment axillary ultrasound scan or indeterminate ultrasound with negative or benign axillary cytology/histology prior to NAC was considered cN0. Univariate analysis (significance at p&lt;0.05) was used to identify risk of recurrence. Patients had a median (mean) follow up of 32.5 (36) months.
Results
The median age at diagnosis was 49 years, median BMI 26, 41 EBC (10%) were screen-detected, 292 (72%) were grade 3 and the most frequent phenotype was receptor triple negative (n=132, 32%).
Of 408 axillae, 248 (60%) were initially cN0, of which 113 (46%) had a pathological complete response (pCR) in the breast. SLN in 54 (22%) cN0 patients were positive on OSNA, of which only 6 (9%) had further involved axillary nodes all 6 of which were ER+ Her2-.
The remaining 160 (40%) axillae were cN1 of which 87 (54%) had conversion to ypN0 including 55 (34%) with both ypT0ypN0.
Axillary lymphadenectomy (AL) was performed in 79 (19%) patients overall, of which n=22 (28%) were cN0 and 57 (72%) were cN1. Of these, 30 (53%) of the cN1 and 6 of 22 (45%) of cN0 had at least 1 additional positive AL node.
Overall 59 (14.4%) patients relapsed. A significantly worse rate of relapse was observed in cN1 compared to cN0 patients (37/159 (23.3%) versus 22/244 (9%), p&lt;0.001). Combined pCR of both breast and axilla (in cN1, n=54) was associated with a significantly reduced risk of relapse and death (p&lt;0.001) compared to those without pCR of either breast or axilla (n=62). Of the latter 18 (29%) relapsed (including 10 deaths).
The mean of both the single highest node tumour load (and total nodal tumour load), as measured by CK19mRNA copies/ul on OSNA, were significantly higher at 90,000 (98,300) for those who relapsed versus 23,100 (25,100) for those without relapse (p=0.027).
Conclusions
The OSNA assay is an accurate tool for axillary SLN analysis in patients after NAC and was helpful in intra-operative axillary management. OSNA reduces the need for a second surgery for AL in 20% of breast cancer patients with a positive-SLN after NAC and might offer additional prognostic value.
Reference
1. NCCN. National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology Breast Cancer.2016.Version 2.2016.
Citation Format: Muscara F, Christaki G, Richardson C, O'Connell R, Padmanabhan P, Warwick J, Lee Y, Smith I, Nerurkar A, Osin P, Krupa K, Rusby J, Roche N, Gui G, MacNeil F, Barry P. Clinical utility of one-step nucleic acid amplification (OSNA) in axillary surgery after neoadjuvant chemotherapy (NAC) [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 P3-03-14.