Abstract PD8-04: Neoadjuvant chemotherapy for breast cancer: Nodal downstaging is highly correlated with pathological complete response

Background: Neoadjuvant chemotherapy (NAC) is employed in patients with larger tumors to attempt to downstage locally advanced cancers to allow breast conservation and to assess in vivo tumor response. The Multi-Institutional Neoadjuvant Therapy MammaPrint Project I (MINT) study asked a secondary question of whether complete nodal downstaging could also be achieved with NAC. Methods: This analysis included 147 eligible invasive breast cancer patients with high tumor burdens, classified as cT2-4N0-3M0 (T2 greater than 3.5cm if N0). Patients who had a positive core biopsy and/or fine needle aspiration (FNA) on an axillary node prior to starting NAC were included in this analysis. Those who had a surgical sentinel lymph node biopsy were not included. Nodal involvement was established following neoadjuvant treatment by axillary lymph node dissection (ALND). Results: This population was 54% postmenopausal, average age 53 yrs (range 25 to 80 yrs). Tumor characteristics were 91% invasive ductal carcinoma; 65% T2, 29% T3, 6% T4; 87% LN1, 13% LN2-3; 3% low grade, 38% intermediate grade, 59% high grade; 65% ER-positive, 49% PR-positive, and 28% HER2-positive by immunohistochemistry; 84% High Risk (HR) and 16% Low Risk (LR) by MammaPrint (MP). After NAC, 45% (66/147) of these LN-positive patients were down-staged to ypN0 and also achieved a complete pathological response in the primary tumor. The potential for down-staging was inversely-related to tumor burden, where 47% (60/128) of N1, 35% (6/17) of N2, and 0% (0/2) of N3 patients were down-staged to ypN0. There were 3 patients who were down-staged (2 N2 to N1, and 1 N3 to N2), but not to ypN0. At surgery, 34% (44/128) of patients had no change, and 19% (24/129) progressed in LN staging. Conclusions: We confirmed that upon achieving a complete response of the primary tumor that there was also a pathologic complete response in the LN. About 53% of patients had no change or progression of LN involvement following NAC. Citation Format: Blumencranz P, Habibi M, Treece T, Blumencranz L, Yoder E, Audeh W, Carter E, McNaughton L, Roussos J, Shivers S, Acs G, Cox C, MINT Investigators Group. Neoadjuvant chemotherapy for breast cancer: Nodal downstaging is highly correlated with pathological complete response [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 PD8-04.