101P Correlation of radiological and pathologic lymph nodes status after neoadjuvant treatment of early HER2-positive breast cancer

The current standard of care for patients with early-stage (T2-3N0) breast cancer (EBC) is neoadjuvant chemotherapy (NAC) followed by breast conserving surgery and sentinel lymph node biopsy (SLNB). After SLNB about 7% of patients observe upper limb or breast lymphedema. The SOUND trial demonstrated the safe refusal of SLNB in postmenopausal women with T1N0 luminal breast cancer 1. We would like to conduct a study on avoiding SLNB in HER-2-positive T2-3N0 patients with complete or expressed clinical response after NACT. We identified patients with T2-3N0 HER2-positive breast cancer treated with NAC followed by surgery at our institution between 8/2019 and 12/2023. Staging including bilateral mammography and ultrasound (US) of both breasts and regional lymph nodes (LNs). We assessed the radiological and pathological response of the tumor to NAC, as well as the status of regional lymph nodes before and after treatment. To determine the therapeutic effect of the tumor, the RCB system was used. Complete data was available for 101 patients. Clinical and pathological characteristics of patients are reported in the table. RCB 0 was achieved in 67/101 (66.4%), RCB I in 14/101(13.8%), RCB II in 20/101(19.8%). In 21 cases was achieved сCR. Breast-conserving therapy was performed in 74 (73.3%) patients, skin-sparing mastectomy in 12 (11.9%) cases, mastectomy in 15 (14.8%) cases. SLNB was performed in 96 (95%) patients, lymphadenectomy in 5 (5%). Intra-operative assessment of LNs was performed in 89 (88.1%). Metastases weren't found in all cases. pN0 was achieved in 100 cases (99%), pN1mic in 1 case (1%).Table: 101PPatient characteristicN=101Age of diagnosis, median45 (31-73)Tumor gradeG10 (0%)G244 (43.6%)G357 (56.4%)LN core-biopsy before NAC9 (8.9%)Suspicious LN before NAC36 (35.6%)Suspitious LN after NAC16 (15.8%)HR+56 (55%)HR-45 (45%)HER2 3+76 (75%)HER2 2+ (FISH positive)26 (25%)Ki67>2084 (83.2%)Ki67<2017 (16.8%)Type of NACddAC + TH34 (33.7%)TCHP22 (21.8%)AC-TH+P45 (44.5%) Open table in a new tab According to our data SLNB could be safely avoided in this cohort of patients. Further studies are needed to determine the feasibility of performing radiological methods in patients with Her2-positive EBC.