Abstract P5-13-06: Biological and clinical changes after neoadjuvant endocrine treatment: Results in a Spanish cohort of 106 patients
Authors: Marti Covadonga , Frias Laura , Loayza Adolfo , Yebenes Laura , Melendez Marcos , Moreno Elisa , Oliver Jose M , Zamora Pilar , Sanchez-Mendez Jose I 
Published: March 2020

Background: neoadjuvant endocrine treatment (NET) has demonstrated to be a useful strategy for downstaging luminal breast cancer as well as to deepen into luminal tumors biology. But, in spite of evidence, NET remains as an under-utilized tool, relegated to elderly frail patients. Purpose: to determine clinical and biological response after NET in luminal breast cancer.Methods: An observational prospective study was performed. Postmenopausal patients with luminal breast cancer T1-3, N0-2 diagnosed between January 2016 and April 2019 were included. They received treatment with letrozole 2,5mg/24h usually for 4-6 months or until maximum response was achieved. A few patients continued treatment further than 6 months because of surgery refusal or contraindication. In the rest of cases, surgery was performed after NET. An intermediate core biopsy (CB) was carried out in those patients with initial Ki67 &gt;10%. Immunohistochemical and conventional pathological studies were made in the initial CB as well as in the intermediate CB and the surgical specimen.PEPI score (PS) was also calculated. Results: a total of 106 patients were included, with an average age of 73.7y [53-90]. 80 (75.5%) were ductal infiltrating carcinomas; 16(15,1%) lobular infiltrating carcinomas. The 10 remaining cases were minority histologic types. 62.3% were luminal B tumors. A positive axilla was present in 16 patients (15.0%). Surgery has been performed in 72 patients. The remaining 33 patients continue treatment nowadays (in 6 of them surgery was dismissed or refused by patient). Breast conserving surgery was feasible in 60 out of 72 (83.3%), although two of these patients chose mastectomy. Average size before treatment was 28.2mm [7.0-90.0], and in the surgical sample (pT) was 15.9mm [4.0-35.0] (p&lt;0.001). Average duration of NET was 4.5 months [1-14]. Statistical differences between Progesterone Receptor (PR) levels before (62.4%) and at the surgical sample (11.1%) were observed. Estrogen Receptor (ER) levels remained stable during and after treatment.Baseline Ki67 average value was 21.4% [3.7-60.0]. The reduction in geometric mean Ki67 levels was statistically significant at both 4 weeks and the surgical sample. In 9/70 patients (12.8%) who had an intermediate biopsy there was no reduction of the Ki67 value. In 55 (75.3%) Ki67 was &lt;=10% after 4 weeks and in 60 (82.1%) in the surgical specimen. There were no statistical differences between luminal A and luminal B tumors in terms of Ki67’s descent.Results of PEPI score (PS)were as follows. PS 0: 41(56.9%); PS 1: 15(20.8%); PS 2: 5 (6.9%); PS 3: 4(5.5%); PS 4: 6(8.3%); PS 6: 1(1.4%). PS was inversely related with initial PR levels (p=0.008) and directly with Ki67 levels after 4 weeks (p=0.036).Axillary involvement was not modified after NET. In all of these cases axillary dissection was performed. NET was well tolerated and no cases of abandonment of treatment were reported.Conclusions: 1. NET is a therapeutic, well tolerated, option in luminal tumors that permits an increase in breast conserving surgery due to a reduction in tumor size.2. No differences between luminal A and luminal B tumors were observed, although low PR levels and higher Ki67 levels after 4 weeks predict a higher PEPI score.3. In vivo response to NET provides information about tumoral behavior as well as eventual resistances to endocrine treatment and it allows further investigation of new drugs. Nevertheless, biomarkers predictors of response are still needed.

Citation Format: Covadonga Marti, Laura Frias, Adolfo Loayza, Laura Yebenes, Marcos Melendez, Elisa Moreno, Jose M Oliver, Pilar Zamora, Jose I Sanchez-Mendez. Biological and clinical changes after neoadjuvant endocrine treatment: Results in a Spanish cohort of 106 patients [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-13-06.