CHARACTERISTICS OF RESPONSE TO NEOADJUVANT CHEMOTHERAPY IN PATIENTS WITH AGGRESSIVE BIOLOGICAL SUBTYPES OF STAGE II–III BREAST CANCER. ORIGINAL STUDY

Goal: To analyze the tumor response to NACT in patients with aggressive biological subtypes of stage II–III breast cancer based on the contemporary scoring systems for residual pathological stage evaluation and the residual cancer burden according to the RCB system.

Materials and methods: A total of 172 women with stage II–III breast cancer of aggressive biological subtypes (triple negative in 34,3 %; HER2‑positive tumors in 28,5 %; luminal B Her2‑negative BC in 37,2 %) were included in this analysis. The median age of the patients was 47 years (24–81 years); сT2 was the predominant tumor size (65,1 %); 69,8 % of patients had regional lymph node involvement; 62,8 % of patients had G3 tumor; Ki67 ≥ 30 % was found in 90,7 % of cases. All patients received neoadjuvant chemotherapy (NACT) with concomitant anti-HER2 blockade in case of HER2‑positive tumors followed by surgery. Morphological assessment included evaluation of the residual pathological stage and the residual cancer burden according to the RCB system.

Results: Total pathological complete response (no evidence of residual invasive tumor in the breast and lymph nodes — tpCR) was observed in 69 of 172 patients (40,1 %), which corresponded to the уpT0N0 pathological stage and RCB class 0. The highest tpCR rate was achieved in patients with HER2‑positive cancer (63 % in non-luminal HER2‑positive subtype and 59.1 % in luminal HER2 + BC) and triple negative cancer (50,8 %). Meanwhile, the tpCR rate in patients with luminal HER2‑negative BC was only 15,6 %, p < 0.0001.

The proportions of the RCB classes in the whole sample were 6,4 % (RCB-I), 30,2 % (RCB-II), 23,3 % (RCB-III), and differed significantly between the biological subtypes. RCB class I was nearly absent in the triple negative cancer group (1,7 % only), the residual tumor corresponded to RCB classes II and III in 25,4 % and 23,7 % of cases, respectively. In the HER2‑positive cancer group, the percentage of patients with RCB class I residual tumors was 9,1 % and 11,0 % in luminal and non-luminal cancers, respectively. One of four patients had RCB class II; RCB class III was found only in 9 % of luminal HER2‑positive cancer cases and in no patients with non-luminal HER2‑positive subtype. Most patients with luminal B HER2‑negative BC had RCB II and III: 39,1 % and 37,5 % of cases, respectively, p < 0.0001.

Conclusions: patients with aggressive biological BC subtypes differed significantly not only in the rates of the total pathological complete response to NACT, but also in the distribution of residual cancer burden classes, which can be translated into the disease prognosis.

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