Abstract PO3-06-01: Factors associated with first- and second- line attrition among metastatic breast cancer patients

Abstract Background: Estimating patient attrition across lines of treatment, i.e., the probability that upon failing one treatment the patient will be able to receive a subsequent treatment, may be a valuable tool for treatment sequencing. We sought to describe first-to-second line (1to2-line) and second-to third line (2to3-line) attrition rate and factors associated with attrition. Methods: The GIM14/BIO-META is an ongoing, ambispective observational multicenter study enrolling breast cancer patients receiving first-line therapy. In progressing patients, attrition was defined as no further anticancer treatment and death within 6 months from the end of the previous line. Attrition from 1to2-line and from 2to3-line was studied by descriptive analyses, factors associated with attrition by univariate ad multivariable logistic models. Results: From January 2000 to December 2021, 3,109 patients with metastatic breast cancer were enrolled in the GIM14/BIO-META study. After the exclusion of 611 patients with ongoing first-line treatment, we included 2,498 patients in the analysis of 1to2-line attrition. Considering tumor subtype, 1,650 (66.0%) patients were diagnosed with metastatic luminal-like, 622 (24.9%) with HER2-positive and 177 (7.1%) with triple negative (TN) tumors. At the time of diagnosis of advanced disease, almost half of the patients (52.0%) had only one involved metastatic site and 45.9% of the patients were diagnosed with visceral involvement. Overall, 1to2-line attrition was 9.0% (224/2,498) with similar attrition for patients with luminal-like (8.5%) and HER2-positive (7.1%) breast cancer. Patients with TN disease experience the highest 1to2-line attrition (13.0%). Age, disease-free interval from primary tumor diagnosis, and type of metastatic spread independently predicted 1to2-line attrition. Univariate analyses of factors associated with 1to2-line attrition among patients with luminal-like breast cancer were similar to those of the entire cohort. Overall, 2to3-line attrition was 14.0% (260/1,861) with higher attrition rates among patients with TN disease (22.7%) compared to patients with luminal-like (13.4%) and HER2-positive (13.0%) breast cancer. Age, tumor subtype, pattern of visceral spread and shorter time-to treatment discontinuation during first-line therapy were independent factors associated with 2to3-line attrition. Conclusions: Pending confirmation in independent series and integration with biomarkers of treatment failure, these results, may provide a valuable support for treatment decisions and clinical research on treatment sequencing. Citation Format: Eva Blondeaux, Luca Boni, Giovanna Chilà, Arianna Dri, Roberta Caputo, Francesca Poggio, Alessandra Fabi, Grazia Arpino, Federico Pravisano, Elena Geuna, Tommaso Ruelle, Irene Giannubilo, Michelino de Laurentiis, Fabio Puglisi, Claudia Bighin, Matteo Lambertini, Filippo Montemurro, Lucia Del Mastro. Factors associated with first- and second- line attrition among metastatic breast cancer patients abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-06-01.