Audit of Targeted Sentinel Node Biopsy (TSNB) in Patients With Limited Nodal Disease Undergoing Primary Surgery

Axillary ultrasound scan (AUS) is routinely employed in the UK for preoperative axillary staging and can diagnose approximately 50 - 80% of node positive patients when combined with percutaneous needle biopsy techniques (either core-biopsy or fine-needle aspiration cytology). It is recognised that nodal burden is generally higher in clinically node negative patients with abnormal nodes on AUS and confirmed on needle-biopsy to be histologically positive than patients diagnosed as node positive on sentinel node biopsy (SNB). However, up to 40% of biopsy-proven node positive patients are found to have fewer than 3 involved nodes on subsequent axillary lymph node dissection (ALND) and are potential candidates for less extensive axillary surgery with axillary radiotherapy (ART) rather than ALND. The total number of abnormal nodes on ultrasound is a key predictor of overall nodal tumour burden.

The AMAROS and OTOASOR trials randomised patients with up to 2 positive sentinel nodes to either ALND or ART. These trials were conducted around the turn of the millennium and before routine use of AUS and therefore would have included a significant number of patients who were radiologically node positive (cN1). Likewise, the ACOSOG Z0011 trial that randomised a similar group of patients to either ALND or observation only, did not incorporate routine AUS and would have included some (radiological) cN1 patients. These trials revealed no adverse impact on disease-free or overall survival from omission of completion ALND.

Targeted axillary dissection (TAD) was introduced a few years ago to reduce the false negative rate of SNB following neoadjuvant chemotherapy (NACT) and has been standardised as part of the ongoing ATNEC trial \[ClinicalTrials.govNCT04109079\]. This technique for axillary staging after NACT is increasingly being adopted in the UK and elsewhere. TAD is technically more straightforward and less challenging in patients undergoing primary surgery with no concerns about clip migration consequent to nodal shrinkage as part of treatment response to NACT. Furthermore, the risk of under-treating the axilla is offset by the protocol: if no disease is identified in the targeted nodes (false-negative case), then patients proceed to ALND, thereby ensuring adequate treatment. Unlike TAD following NACT, the presence of viable tumour within the sampled nodes is mandatory and finding fibrosis is irrelevant except as a response to nodal biopsy per se.

Current ASCO guidelines support both SNB and TAD as staging options for patients with ultrasound-detected, biopsy-confirmed nodal disease. The Edinburgh randomised trials comparing four-node sampling with ALND demonstrated significantly lower arm morbidity with node sampling, supporting TAD as a less morbid appropriate alternative in this patient population.

The UK-ANZ POSNOC trial randomised 1,900 patients with \<3 macrometastases to either no further axillary treatment or additional axillary treatment. The study included cN1 patients with biopsy-confirmed nodal metastases who underwent sentinel node biopsy or TAD. Patients with \<3 macrometastases on final histology were randomised to receive no further axillary treatment or proceed with additional axillary treatment (ALND or ART). POSNOC trial will answer whether further axillary treatment provides any benefit in patients with low volume nodal disease on SNB or TAD.

Notably, patients with biopsy-confirmed metastases and \<3 macrometastases on SNB/TAD are biologically and clinically similar to patients with normal AUS who are later found to have low-volume disease on SNB. Clinical decision-making and patient outcomes are driven by tumour biology and overall disease burden rather than the method of nodal disease detection. Furthermore, AUS sensitivity is operator dependent and whether FNA or core biopsy was used to sample the node. A patient considered node negative on AUS by one radiologist may be diagnosed with core biopsy confirmed nodal metastases with another radiologist. Pending the results of POSNOC trial, patients with less than 3 macrometastases are generally advised further axillary treatment, and ART is preferred over ALND to reduce the risk of lymphoedema.

NodeSMART is a prospective audit collecting data on patients undergoing TAD in the primary surgery setting. Its goal is to audit surgical outcomes and benchmark them against - a) Comparing technical outcomes with those from sentinel node biopsy in the primary surgery setting and TAD performed after neoadjuvant chemotherapy. b) Assessing rates of arm lymphoedema and disease progression relative to findings from the AMAROS and Z11 trials, and the POSNOC trial once results are available. The term "Targeted Axillary Dissection" is somewhat misleading in this context, as the marked (biopsied) node is removed alongside sentinel nodes - not in isolation. NodeSMART therefore refers to the procedure more accurately as Targeted Sentinel Node Biopsy (TSNB).