Abstract P4-06-03: Pathological complete response (ypCR) in early and locally advanced breast cancer (LABC) patients treated with neoadjuvant chemotherapy in a middle-income country. Results from a real-world historical cohort

Abstract Introduction Breast cancer (BC) is the most frequent neoplasm in Colombia, with mortality rate increasing in past decade. The expected 5-year overall survival (OS) is < 80%, being the Latin American country with the worst prognosis. 2 factors related to this are higher frequency of advanced stages and higher frequency of aggressive tumor subtypes.Neoadjuvant chemotherapy (NACT), and ypCR, have demonstrated impact on the risk of relapse and death. This trial describes the characteristics, treatment patterns, clinical outcomes, and ypCR after NACT in a cohort of Colombian BC patients. Methods We included BC adult patients treated with NACT in 3 institutions in Colombia. Clinical, sociodemographic, and outcome variables were retrieved retrospectively from clinical charts. Univariate, bivariate and time-to-event analyses were performed. A partition survival tree was performed to explore interactions between variables. Statistical analyses were done in R software.The protocol was approved by the IRC and EC of Fundación Cardioinfantil and Hospital Militar Central. Results We included 312 patients treated between 2013 and 2019. 50.9% were ER and/or PgR positive, 28.5% HER2 positive and 20.5% triple negative breast cancer (TNBC). 75.9% of the patients had a LABC. TNBC patients were younger (median age 46 years), premenopausal (58%), had higher Ki67 index (Ki67 ≥ 20%= 91%), and a higher tumor grade (Grade 3= 56.7%). Most of the patients (91.7%), received Doxorubicin + Cyclophosphamide, and Taxanes (97.8%), 76.6% of TNBC patients received Carboplatin. Breast conserving surgery was performed in 53.7% of the patients, and only 38.9% received immediate breast reconstruction. 88.5% of the patients were treated with adjuvant radiotherapy. The ypCR rate was 34.6% and was achieved more frequently in HER2 positive subtype. The ypCR rates in TBNC were higher in patients treated with carboplatin (55% vs 20%, p=0.02). Other factors related to ypCR were high Ki67 (p= 0.0005) and higher tumor grade (p= 0.0034). Most of the relapses were distant (14.1%), with only 1.9% of local relapse rate. Table No 1 summarizes clinical outcomes. With a median follow up of 4.9 years, the 5 year OS was 88.2%. Clinical stage at diagnosis (p= 0.01); node involvement (p= 0.0014); ER (p= 0.0032); PgR (p= 0.0069); HER2 (p= 0.0334); phenotype (p=0.0145); type of surgery (p< 0.0001); ypCR (p=0.003); and relapse (p= < 0.00001) were related with OS. We did not found differences in the 5 year OS between stage II and III patients (87.8% vs 88%). The 5 year OS did not differ between ypCR and ypCR-IS (94.2% vs 93%). The relapse rate was 3.7% in ypCR vs 22.1% in non ypCR patients (p< 0.00001). The 5 year OS rate was 94.3% for ypCR and 85% for non ypCR patients (p= 0.0059). When analyzed by phenotype, ypCR was only related to risk of death among TNBC (p= 0.011). We perform a partition survival tree, identifying 6 subgroups with different OS behaviors: TNBC and non TBNC; low proliferative and high proliferative; early stage and locally advanced stage. Discussion We found an increased number of LABC. The ypCR rate was higher than described elsewhere, explained by higher proportion of TNBC and HER2 enriched tumors and differences in treatment selection in subgroups. In the TNBC subgroup the use of carboplatin was associated with higher ypCR. ypCR was related with risk of death and relapse, but with statistical significance for OS only in the TNBC population. This study offers a baseline characteristic of NACT BC cohort, that will allow us to design and implement strategies to improve outcomes in early and LABC. Table 1: Treatment outcomes by phenotype. Citation Format: William Mantilla, Maria-Fernanda Gonzalez, Sebastian Rojas, Mariana Borras-Osorio, Nicolas Molano-Gonzalez, Joaquin Guerra, Isabel Munevar, Diego Moran. Pathological complete response (ypCR) in early and locally advanced breast cancer (LABC) patients treated with neoadjuvant chemotherapy in a middle-income country. Results from a real-world historical cohort. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-06-03.