Abstract P2-16-06: In-breast pathologic complete response (pCR) following neoadjuvant chemotherapy predicts nodal pCR in early stage breast cancer
Authors: Shamseddine Achraf , Flynn Jessica , Zhang Zhigang , Morrow Monica , Mueller Boris , Gillespie Erin , Khan Atif , McCormick Beryl , Cahlon Oren , Powell Simon , Barrio Andrea , Braunstein Lior Z 
Published: March 2020

Abstract
Background: With advances in neoadjuvant chemotherapy (NAC), an increasing number of breast cancer patients achieve a pathologic complete response (pCR). Efforts are underway to non-invasively identify pCR in the breast, such that characterization of the concomitant nodal response will be invaluable for locoregional treatment planning. Here, we sought to evaluate the correlation between in-breast response and residual nodal disease among early stage breast cancer patients.
Materials/Methods: We identified 728 patients who received NAC at our institution from 2006 to 2016. Breast and nodal response rates were evaluated and further stratified by clinicopathologic features, and biologic subtype approximation (hormone receptor positive [HR+], HER2 negative [HER2-] and low or intermediate grade = luminal A; HR+/HER2- and high grade = luminal B; HER2/neu-amplified = HER2+; ER-/HER2- = triple negative). Descriptive statistics and univariate analyses were employed to evaluate the correlation between breast and nodal response.
Results: Of 728 patients, 269 (37%) were clinically node negative (cN0) and 459 (63%) were clinically node positive (cN+). Median age was 51 and median tumor size was 4.0cm (IQR 2.7 - 5.5cm). The cohort comprised 13% luminal A patients, 20% luminal B, 38% HER2, and 29% triple negative. Following NAC, the overall pCR rate (breast and nodes) was 29.8%. Among all cN0 patients who had a breast pCR (ypT0; n = 96), none exhibited residual nodal disease (100% ypN0). Among cN+ patients who had a breast pCR (n = 128), only 5.4% (n = 7) had residual nodal disease (ypN+). Rates of residual nodal disease among cN+ patients who achieved breast pCR varied by biologic subtype: luminal A patients with pCR in the breast had a 50.0% probability of residual nodal disease (n = 1/2 were ypT0N+), luminal B 6.7% (1/15), HER2+ 2.5% (2/80) and triple-negative 9.6% (3/31) (p=0.03).
Conversely, among cN+ patients who exhibited nodal pCR following NAC, the rate of residual in-breast disease varied by receptor subtype: 80.0% of clinically node-positive luminal A patients who became ypN0 had residual in-breast disease (ypT+N0; n = 4/5), 60.0% of luminal B (21/35), 38.1% HER2+ (48/126), and 50.9% triple negative (29/57) (p=0.03).
Conclusions: Among early stage breast cancer patients receiving NAC, in-breast pCR is predictive of nodal pCR. Among 96 cN0 patients who had in-breast pCR, we found none with residual nodal disease, representing a population that may be suitable for further limiting nodal therapy. The ability to pre-operatively identify in-breast pCR in this population would be particularly valuable if nodal pCR can consequently be inferred, potentially paving the way for studies of therapeutic de-escalation.
Citation Format: Achraf Shamseddine, Jessica Flynn, Zhigang Zhang, Monica Morrow, Boris Mueller, Erin Gillespie, Atif Khan, Beryl McCormick, Oren Cahlon, Simon Powell, Andrea Barrio, Lior Z Braunstein. In-breast pathologic complete response (pCR) following neoadjuvant chemotherapy predicts nodal pCR in early stage breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-06.