Features of p53 expression in residual tumors in Russian women after neoadjuvant chemotherapy of breast cancer stage T1-3N0-1.

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e12121 Background: Residual tumor is an important prognostic factor after neoadjuvant therapy, however, p53 expression in the residual breast tumors poorly understood. Methods: In our study included 164 Russian women (24-76, median age - 47) with breast cancer stage T1-3N0-1 treated in RCRC from 2004 to 2016. Biological subtype of primary tumor was luminal A (8,1%), luminal B HER2-negative (43,6%), luminal HER2+ (15,4%), triple negative (22,8%) and non-luminal HER2+ (10,1%). After neoadjuvant chemotherapy by anthracycline ± taxanes (in HER2+ cancer ± trastuzumab) patients had radical surgery. We analyzed pathological response after neoadjuvant therapy and features of p53 expression in residual tumors. Results: The rate of pCR was 23% for all women, and was a very various for biological type (luminal A – 0%, HER2- luminal B - 11%, HER2+ luminal - 38%, triple negative – 35% and HER2+ non-luminal - 50%), p=0,003. In 15% cases pathological response was a very similar to pCR, in 62% - was low. In analyze of 38 residual tumors we found p53 low expression (<10% stained cells) in 66% cases and high (>10% stained cells) - in 34%. We did not find any correlation between p53 rate in residual tumors and stage, Ki67 and PR-status (p>0,05). But p53 expression strongly correlated with age, tumor grade and biological type (p<0,05). So, high rate of p53 was found more often in women <45 years (50%) vs women 45-59 years (15,4%) and patients 60 years older (20%), p=0,04. All G1-tumors was p53-negative, p53 high expression was seen in 29% of G2 tumors and 80% - G3, p=0,04. The high rate of p53 residual tumor was seen in luminal A subtype in 0%, HER2- luminal B – 30%, HER2+ luminal – 75%, triple negative -50%, HER2+ non-luminal - 100%, p=0,01. Conclusions: High expression of p53 in the residual tumors after neoadjuvant chemotherapy is associated with younger age and unfavorable biological characteristics that may be a very important for the further prognosis in breast cancer.