Abstract PS6-54: Prognostic significance of residual micrometastatic axillary involvement with complete pathologic breast response after neoadjuvant chemotherapy for early breast cancer
Authors: García-Torralba Esmeralda , Garcia Maria Esperanza Guirao , de la Morena Barrio Pilar , Rubio Alejandra Ivars , Martinez Elena Garcia , Garre Elisa Garcia , Zafra Gema Marin , Abril Beatriz Alvarez , Manzano Esther Navarro , Ayala de la Peña Francisco 
Published: February 2021

Introduction and objectives Pathologic complete response (pCR, ypT0/Tis ypN0) after neoadjuvant chemotherapy (nCT) in early breast cancer (BC) is associated with higher survival rate. Controversy about the prognostic significance of low-volume or micrometastatic axillary residual disease (ypN1mi-RD) exists. Essentially, it is considered equivalent to high-volume nodal disease (ypN1/ypN2-RD) for the indication of lymphadenectomy after nCT. Clarifying ypN1mi-RD prognostic value would be useful for planning adjuvant therapy. Thus, our objective was to assess the prognostic significance of ypN1mi-RD in the context of primary breast tumor pCR. Material and methodsRetrospective, single-center analysis of a cohort of early BC patients treated with nCT between 2010 and 2018 who achieved breast pCR (ypT0/Tis) combined with axillary pCR (ypN0) or ypN1mi-RD or ypN1/ypN2-RD. Cases with pre-nCT sentinel lymph node biopsy were excluded. 5-year disease-free survival (DFS) and overall survival (OS) were analyzed using Cox regression models.ResultsAmong 470 early BC patients treated with nCT, 134 (28.5%) had in-breast pCR, of whom: 97 (20.6%) were ypN0; 7 (1.5%) were ypN1mic; 10 (2.1%) were ypN1 and 5 (1.1%) were ypN2. Clinicopathological characteristics of the groups are shown in the Table. Median follow-up: 33 months. Eight patients relapsed, 4 of 97 with nodal pCR and 4 of 22 with axillary residual disease: 2/7 ypN1mic; 1/10 ypN1 and 1/5 ypN2. Patients who relapsed predominantly presented pre-nCT clinical lymph node involvement, hormone receptor negativity, ki67&lt;20% and absence of complete clinical response (100%). Globally, patients with axillary residual disease had lower DFS rates (95% vs. 69%, p = 0.03), with no apparent differences between ypN1-RD vs. ypN2-RD in the subgroup analysis (75% vs. 80%, respectively). ypN1mic-RD patients showed the poorest DFS (33%, p &lt;0.01). In the multivariable analysis, ypN1mic-RD had worse DFS than nodal pCR (HR 13.98, 95%CI 1.95-100.24, p = 0.01), but no differences were observed between the low and high-volume residual axillary disease categories (HR 0.24, 95%CI 0.03-1.74, p = 0.16). Due to the low rate of events, no differences in terms of OS were observed (p = 0.77).Conclusion In the context of in-breast pCR after nCT for early BC, ypN1mic-RD not only presented a higher risk of relapse than nodal pCR, but also was not associated with a better prognosis than that observed for ypN1/ypN2-RD. Micrometastatic axillary residual disease behaves as an independent adverse prognostic factor, comparable to high-volume axillary residual disease, and might be considered as a factor for the indication of post-nCT adjuvant treatment.

Table. Clinicopathologic characteristics of the cohort of early BC patients treated with nCT betweenypT0/TisypT0/TisypN1mic-RDypN1/N2-RDpCR(N=7)(N=15)(N=97)Age (median, range)49 (25-83)47 (40-77)47 (25-80)Menstrual statusPostmenopausal3 (42,8%)4 (26,7%)42 (43,3%)Premenopausal4 (57,1%)11 (73,3%)55 (56,7%)ECOGECOG 05 (71,4%)13 (86,7%)78 (80,4%)ECOG 12 (28,5%)2 (13,3%)19 (19,6%)Histologic subtypeInvasive ductal carcinoma7(100,0%)14 (93,3%)95 (97,9%)Other subtypes0 (0,0%)1 (6,7%)2 (2,0%)Histologic gradeGrade 10 (0,0%)0 (0,0%)1 (1,0%)Grade 23 (42,9%)5 (33,3%)17 (17,5%)Grade 34 (57,1%)8 (53,3%)67 (69,1%)Unknown0 (0,0%)2 (13,3%)0 (0,0%)cTcT11 (14,2%)4 (26,7%)8 (8,2%)cT24 (57,1%)5 (33,3%)63 (64,9%)cT32 (28,6%)6 (40,0%)24 (24,7%)cT4a-d0 (0,0%)0 (0,0%)2 (2,1%)cNcN01 (14,3%)0 (0,0%)27 (27,8%)cN13 (42,9%)5 (33,3%)34 (35,1%)cN21 (14,3%)6 (40,0%)24 (24,7%)cN32 (28,6%)4 (26,7%)11 (11,3%)Molecular subtypeHR+ HER2-1 (14,3%)8 (53,3%)11 (11,3%)HR+ HER2+3 (42,9%)1 (6,7%)30 (30,9%)HR- HER2+2 (28,6%)3 (20,0%)21 (21,6%)TNBC1 (14,3%)3 (20,0%)35 (36,1%)Breast surgeryConservative7 (100%)10 (66,7%)67 (69,1%)Mastectomy0 (0,0%)5 (33,3%)30 (30,9%)Nodal surgerySLN biopsy0 (0,0%)0 (0,0%)22 (22,7%)ALND7 (100,0%)15 (100,0%)75 (77,3%)ypTypT05 (71,4%)7 (46,7%)80 (82,5%)ypTis2 (28,6%)8 (53,3%)17 (17,5%)Relapse typeMetastatic2 (28,6%)2 (28,6%)2 (2,1%)Local/contralateral0 (0,0%)0 (0,0%)2 (2,1%)Deaths0 (0,0%)1 (6,7%)1 (1,0%)BC: breast cancer. HR: hormone receptor. nCT: neoadjuvant chemotherapy. pCR: pathologic complete response. SLN: sentinel lymph node. TN: triple negative. ypN1mic-RD: micrometastatic axillary residual disease. ypN1/N2-RD: high-volume axillary residual disease.

Citation Format: Esmeralda García-Torralba, Maria Esperanza Guirao Garcia, Pilar de la Morena Barrio, Alejandra Ivars Rubio, Elena Garcia Martinez, Elisa Garcia Garre, Gema Marin Zafra, Beatriz Alvarez Abril, Esther Navarro Manzano, Francisco Ayala de la Peña. Prognostic significance of residual micrometastatic axillary involvement with complete pathologic breast response after neoadjuvant chemotherapy for early breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-54.