PROGNOSTIC CRITERIA DETERMINING A COMPLETE PATHOMORPHOLOGICAL RESPONSE DURING NEOADJUVANT SYSTEMIC THERAPY OF HER2+ BREAST CANCER»

Krivokhizhin Igor Viktorovich, Parsadanyan Ararat Mikichovich

Background: neoadjuvant systemic therapy plays a key role in the combined treatment of HER2-positive breast cancer (BC). In this regard, it is of particular importance to identify prognostic factors that make it possible to assess the effectiveness of treatment, as well as to determine the optimal criteria for assessing the tumor response. Aim: the purpose of the current study was to analyze and determine the most significant prognostic criteria for achieving pathological complete response (pCR) during preoperative HER2+ breast cancer therapy. The morphological response was assessed using the RCB (Residual Cancer Burden) system, and additional characteristics of the residual tumor were studied. Materials and methods: a randomized retrospective study of 175 breast cancer patients with HER2 positive subtypes of stage II and III receiving neoadjuvant systemic therapy was conducted. The treatment took place on the basis of the Surgut District Clinical Hospital in a day hospital for surgical treatment and antitumor drug therapy from 2019-2023. Statistical data processing was performed using the SPSS statistics software version 27.0.1. Results: as a result of the data obtained, we found out that the frequency of achieving pCR in T1 (77.8%), T2 (51.5%), T3 (31.3%). No statistically significant results were achieved depending on regional metastasis (cN) and the frequency of achieving a complete response to treatment (p=0.11). At stage IIA, the incidence of pCR reached 59.2%, stage IIB – 52.9%, and at stage IIIA - 35.7% (p=0.041). In comparison of luminal and non-luminal tumors, statistical significance was obtained for pCR (p<0.001). In luminal HER2+ patients, the incidence of complete therapeutic pathomorphosis was lower (32.5%) compared to non–luminal ones (64.1%). We also obtained the statistical significance of the frequency of pCR depending on the level of Ki-67 (p=0.032). With a Ki value of 67, 45% or more is expected to achieve a pCR. Conclusions: the results of the study demonstrate that an integrated approach makes it possible to identify prognostic groups of patients based on clinical and morphological factors and optimize the choice of adjuvant therapy tactics on an individual basis.

Keywords:HER2+ breast cancer, prognostic criteria, RCB, Ki-67, pathological complete response, targeted therapy.