Neoadjuvant endocrine therapy (NET) is indicated for treatment of invasive breast carcinomas of luminal subtypes (RH+/HER2-) in locally advanced stages. Several previous randomized studies have shown the benefit of aromatase inhibitors (AI) in this context. However, in care practice, NET has been reserved for cases of elderly or frail patients, where neoadjuvant chemotherapy (NAC) would be too aggressive. Ideally, after identifying the best candidates for NET, the patient should undergo tumor re-biopsy after 2 to 4 weeks of treatment, and only patients with tumors with Ki67<10% should follow NET. Some limitations of this strategy are the standardization of the re-biopsy and the reliability of the analysis by immunohistochemistry of ki67 in the re-biopsy, since the management is modified depending on this analysis. During the COVID-19 pandemic, several experts and medical societies suggested increasing the number of patients undergoing NET, due to less toxicity compared to chemotherapy, less need to come to the hospital, and especially the possibility of postponing the surgical procedure to a more opportune moment. Thus, several dozen patients have been submitted to NET at the Hospital de Amor (Barretos). This retrospective study aims to analyze the cases treated with NET from the clinical point of view and the response to treatment. Special attention will be given to the evaluation of KI67 protein expression in the initial biopsy as well as in the surgical specimen, in order to standardize such analysis for future studies. Keywords: breast neoplasms; therapeutic response; hormone therapy; neoadjuvant treatment; cell proliferation.
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