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e12580 Background: Axillary lymph node dissection is a redundant method of surgical treatment and axillary staging for a large number of patients receiving neoadjuvant therapy with positive lymph nodes before NCT. Methods: The study included 212 patients with breast cancer (cT1-3N1M0) who received treatment at the breast tumors department of the N.N. Petrov NMRC of Oncology from 2019 to 2021 All patients included in the study had the cN1 initial status of the axillary lymph nodes. All patients underwent neoadjuvant systemic therapy and subsequent sentinel lymph node biopsy (SLNB). In patients with pathomorphologically proven metastatic lymph nodes (cN1) even at the initial diagnosis, lymph node marking was performed before the start of NCT and targeted axillary lymph node dissection after the completion of neoadjuvant systemic therapy. In the same patients, after SLNB and targeted axillary lymph node dissection, a complete (standard) axillary lymph node dissection was performed to determine the false-negative rate and the oncological safety of the procedure. Results: The identification rate of only one sentinel lymph node was 21% (40 out of 193 patients), two sentinel lymph nodes - 30% (58 out of 193 patients), more than 3 - 49% (95 out of 193 patients). When only 1 sentinel lymph node was found, the false-negative rate of SLNB was 20.0% (4 of 20) (95% CI, 5.7 to 43.7). When two sentinel lymph nodes were found, the false-negative rate of SLNB was 20.0% (6 of 30) (95% CI, 7.7 to 38.6). When three sentinel lymph nodes were found, the false negative rate of SLNB was 4.7% (2 of 43) (95% CI, 0 to 15.8). Among 45 patients who had a microseed with the iodine-125 radioisotope installed before the start of treatment, the frequency of identifying a marked node was 100%. In 19 patients, tumor cells were found in the lymph nodes. The false-negative rate of targeted axillary dissection in combination with SLNB was 5.3% (1 of 19) (95% CI, 0 to 26.0). Conclusions: Targeted axillary dissection and sentinel lymph nodes biopsy, provided that 3 SLNs are removed, are reliable methods for identifying patients in whom systemic therapy is guaranteed to achieve complete response of regional lymph nodes (ypN0), thereby relieving patients of the need to perform a crippling complete axillary lymph node dissection. Clinical trial information: 3/198.

e12616 Background: Neoadjuvant chemotherapy (NCT), Triple-negative breast cancer (TNBC) including anthracyclines and taxanes for early stages of TNBC, allows to achieve pathological complete response (pCR) in 25-36% of patients. Pathological complete response (pCR) significantly correlates with an increase in disease-free survival (DFS) and overall survival (OS). Methods: Randomized, monocentric trial was conducted in NN Petrov National Medical Research Center of Oncology from 2016 to 2019. 99 patients aged from 28 to 68 years with confirmed TNBC were included in trial: 96 had invasive ductal carcinoma G3, 3 - metaplastic cancer, negative BRCA mutations (a test for Founder mutations was performed).Patients were randomized in 3 groups, depending on the NCT regimen:1st subgroup (24 patients) - Eribulin in combination with Carboplatin AUC 5 x 4 cycles 2nd subgroup (37 patients) - Paclitaxel in combination with Carboplatin AUC 5 x 4 cycles 3rd subgroup (38 patients) –Carboplatin AUC5 + Doxorubicin + Paclitaxel x 6 cycles. Patients 1 and 2 subgroups in an adjuvant mode received 4 cycles of AC. Results: Clinical complete response (cCR) by physical examination (palpation) was achieved in 44 out of 99 patients (44.4%). Clinical complete response (cCR) by ultrasound and MG - in 27 (27.2%) patients. Miller-Payne V regression stage was achieved in 55 out of 99 cases (55.6%). In clinical cT1-T2 stage (n = 70), ypCR was achieved in 49 cases (70%), cT3-T4 (n = 29) ypCR in 6 patients (20.68%). Before NCT, 71 patients had status cN0-N1. Conversion to ypN0 occurred in 57 patients (80.2%). In 28 patients with cN2-N3 status, conversion to ypN0 occurred in 7 patients (25%). The median follow-up was 58 months. Progression was observed in 15.1% of patients, mortality – 6%. Local recurrence - 6 patients (6%), all patients were with residual tumor after NCT. Distant recurrence – 8 patients (8.1 %). Local recurrence rate and distant recurrence rate did not correlate with type of surgery (BCS or ME), but correlated with ypCR. Conclusions: NCT for TNBC is advisable both for locally advanced breast cancer and early breast cancer BC. De-escalation of BC surgery is possible in the future, especially in cT1-T2 stage patients (n = 70) where ypCR rate reaches 70%. It is planned to continue the trial with the vacuum aspiration biopsy of the tumor bed and SLNB after NCT.SLNB after NCT is advisable only in cN0-N1 group of patients (n = 71), since conversion to ypN0 was achieved in 57 patients - 80.2%.

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e12097 Background: Innovative advances in neoadjuvant systemic and targeted breast cancer therapy implicate surgical treatment in specific patient groups can be avoided. The core biopsy of the tumor bed and some diagnostic approaches (breast ultrasound, mammography, SPECT/CT) allow for precise evaluation of the treatment efficacy. Methods: This research started in our department in 2018, we picked two groups of 15 patients each treated for locally advanced TNBC or grade cT1-4N1-3M0 HER2-positive breast cancer: HER2+/ER+ or HER2+/ER- breast cancer. The TNBC group received 6 cycles of NACT of paclitaxel combined with doxorubicin and carboplatin AUC5. The HER2+ group received 4 cycles of АС polychemotherapy followed by 4 cycles of monochemotherapy with the docetaxel and 3-weekly trastuzumab. The HER2+ group is receiving adjuvant trastuzumab for up to one year, where ER-positive patients are also given hormone therapy with tamoxifen or aromatase inhibitors. The response to neoadjuvant treatment was assessed in all patients using standard two-dimensional mammography, ultrasound elastography, and SPECT-CT. The 12-point core biopsy of a tumor bed was performed in the operating room setting by previously marked tumor projections. Then, all patients underwent either breast-conserving surgery or mastectomy with immediate reconstruction with expander/implant. Results: After neoadjuvant therapy, in a group of 15 patients with TNBC in surgically obtained material, the pathologic complete response (pCR) was observed in 8 patients (53.33%), whereas residual disease was found in 7 (46.67%) patients. The core biopsy results showed no tumor cells in 10 (66.67%) patients, and were detected in 5 (33.33%) patients (p = 0.0011), the accuracy of the method in this group was 80%. The overall response rate in the group of 15 patients with HER2-positive breast cancer was 8 (53.33%) patients with residual disease and 7 (46.67%) patients with pCR. According to core biopsy, tumor cells were present in 3 (20%) patients and were absent in 12 (80%) patients (p = 0.0787). Conclusions: Avoiding surgical treatment through not less than 12-point core biopsy of a tumor bed in patients with complete regression after neoadjuvant therapy is a new trend in the treatment of breast cancer. Any new approach in this sphere requires a long-term elaboration, compliance with the safety principles, rethinking standard procedures and following-up patients.