Features of response to modern neoadjuvant chemotherapy with dual anti-HER2 blockade (trastuzumab and pertuzumab) in the patients with HER2-positive breast cancer stage II–III

Background. Neoadjuvant chemotherapy (NACT) with dual anti-HER2 blockade has become a priority in the treatment of patients with HER2+ breast cancer (BC) stages IIIII. However, the question of the accordance of various systems for assessing tumor response to NACT, as well as identifying predictor factors for achieving a complete pathomorphological response (pCR) in HER2+ BC remains open. Aim. To assess the accordance of various systems for assessing tumor response to neoadjuvant chemotherapy (NACT) in patients with HER2+ BC and to identify predictor factors for achieving pCR and residual cancer burden. Materials and methods. The study included 49 women with HER2+ BC stage IIIII, who underwent NACT with anti-HER2 blockade, followed by surgical treatment and morphological analysis of the results. The median age of the patients was 47 years; 91.8% had tumor size T2, N+ status 71.4%; tumor grade G3 73.5%, luminal and non-luminal HER2+ subtype 44.9 and 55.1% of patients, respectively. Ki6730% was observed in 93.9% of cases, the level of TILs in the tumor was 10%, 1020% and 20% in 38.1, 9.5 and 52.4% of cases, respectively. The patients received combinations of anthracyclines and taxanes or the anthracycline-free regimen of docetaxel + carboplatin; 87.8% of patients received a dual blockade of trastuzumab + pertuzumab, and 12.2% trastuzumab. After the end of NACT, all patients underwent a radical surgery (mastectomy or breast-conserving) with an assessment of the pathomorphological response, the pathomorphological stage of ypTN, and the residual cancer burden according to the RCB system. Results. The rate of complete pathomorphological response (tpCR/RCB-0/ypT0N0) in HER2+ BC was 61.2%; significant predictors of achieving tpCR were only 3 factors: primary operable BC stages (T13N01) the rate of tpCR was 71.4%, the level of TILs20% the proportion of tpCR reached 95.5%, and the dual anti-HER2 therapy (trastuzumab + pertuzumab) tpCR was 65.1%. Residual tumor was presented by classes RCB-I, RCB-II, RCB-III in 10.2, 24.5, 4.1%. The RCB-I class included of patients with a residual tumor less than 1.0 cm in the absence of regional lymph node involvement (80% of cases); class RCB-II was represented by the presence of a residual tumor less than 2.0 cm in combination with the absence or presence of residual metastases in 13 lymph nodes (83.4%), and class RCB-III was presented the residual tumors 2.0 cm and N12 status in 100% of cases (p0.0001). Conclusion. Modern NACT with dual anti-HER2 blockade (trastuzumab + pertuzumab) are highly effective the rate of tpCR is 61.2%, and in the presence of high TILs20% reaches 95.5%. Residual tumor in most cases was presented by class RCB-I or RCB-II, only 4% of patients had massive residual tumor load (class RCB-III).