P1: Axillary dissection is avoidable in the majority of cT1N0 triple negative and HER2+ breast cancers having upfront surgery with adjuvant radiation

Introduction: The use of neoadjuvant chemotherapy (NAC) in cT1N0 patients with triple negative (TN) or HER2 positive (HER2+) patients is controversial, pitting the advantage of determining systemic therapy based on pathologic stage against use of adjuvant therapy for those without pathologic complete response (pCR). It is also unclear whether NAC or upfront surgery minimizes risk of axillary dissection (ALND). We sought to determine nodal burden and rates of ALND in this population.


Methods: Consecutive patients with cT1N0 TN/HER2+ breast cancer treated from 1/2020-12/2021 were identified. Those with nodal disease detected by preoperative biopsy were excluded. ALND was indicated for any positive sentinel lymph nodes (+SLNs) after NAC, for ≥3 +SLNs in patients having upfront BCS or mastectomy, or for patients with 1-2 +SLNs having upfront mastectomy not meeting criteria for postmastectomy radiotherapy (PMRT). Clinicopathologic features, nodal burden, and need for ALND were compared between patients who received NAC vs upfront surgery.


Results: Of 380 patients, 160 (42%) were TN and 220 (58%) were HER2+; 30 (8%) patients received NAC followed by surgery, 256 (67%) had upfront breast-conserving surgery (BCS), and 94 (25%) had upfront mastectomy. Recipients of NAC had cT1c tumors, were younger, had more TN cancers, and less often had LVI; other features were similar. Axillary ultrasound was performed in 27% NAC vs 26% upfront BCS vs 32% upfront mastectomy patients, and with similar frequency of benign vs abnormal nodes (Table). Most patients (88%) were node negative, while 11% had 1-2 +SLNs and 1.6% had ≥3 +SLNs. ALND was indicated for 2 (6.7%) patients who had any +SLN after NAC, as compared to 5 (1.9%) patients who had upfront BCS and 1 (1.1%) patient who had upfront mastectomy with ≥3 +SLNs or 1-2 +SLNs not meeting PMRT criteria (p=0.2). On univariate analysis with multiple comparison correction, no factors were significantly associated with ALND, including T stage (T1a-b: ref; T1c: odds ratio [OR] 2.2 [0.5, 13], p=0.3), upfront surgery (NAC: ref, upfront BCS: OR 0.3 [0.06, 2.0], upfront mastectomy: OR 0.2 [0.01, 1.6], p=0.3) or subtype (TN: ref, HER2+ 1.2 [0.3, 6], p=0.8).


Conclusions: ALND was required by < 2% of cT1N0 TN/HER2+ patients having upfront surgery, with no clear advantage of NAC in further reducing risk of ALND in this cohort. Upfront surgery is a suitable approach in these patients, allowing for de-escalated chemotherapy regimens in pathologic node-negative patients.