Abstract PS7-35: Geicam/2014-03 (registem): A prospective registry of advanced breast cancer: A subset of triple negative breast cancer patients with her2 low expression
Authors: Jara Carlos , Álvarez Isabel , Rodríguez César A , Martínez Purificación , Andrés Raquel , Rodríguez-Lescure Álvaro , Malón Diego , Alonso Jose Luis , Adrover Encarna , Echarri María José , Margeli Mireia , Tibau Ariadna , Ramírez Judith , Antolín Silvia , Campo Ruth , Miralles Juan José , Bezares Susana , Rojo Federico , López-Tarruella Sara , Guerrero-Zotano Angel 
Published: February 2021

Background: The RegistEM study will provide prospective data from advanced breast cancer (ABC) patients (pts). Understanding the real distribution of BC subtypes is its primary objective. A new nomenclature has been proposed for those cases with HER2 1+ or 2+ by immunohistochemistry and negative in situ hybridization, HER2-low BC. In clinical practice, these tumors are reported as HER2 negative. Methods: This is a non-interventional study that will enroll approximately 1,867 pts with ABC diagnosed from January 2016 to December 2019, either after recurrence or as 1st diagnosis, in 38 Spanish sites. Biological samples (primary and/or metastatic tumor lesions, and blood) collection is part of its procedures. In this analysis (cut-off date 01/April/2020, database ongoing), we describe the characteristics of pts with Triple Negative (TN) subtype and HER2-low expression (as mentioned above). Biomarkers, including HER2, were determined in either primary tumor (PT), M1 or in both, PT and M1. Results: This subset of pts make up 37.4% (n=49) of TN pts considered for this analysis (n=131). Their distribution within the three groups (PT, M1 and PT/M1), was 46.9% (n=23), 42.9% (n=21) and 10.2% (n=5), respectively. These pts were diagnosed with early BC (EBC) and at recurrence, 91.7% presented distant metastases. Median time from EBC diagnosis until recurrent disease in terms of ABC was 29.8 months (mo), with the majority of pts recurring at &gt;12 mo (95.9%), similar to the whole TN subset. Most pts were Caucasian (98%), and at diagnosis of ABC, the median age was 60 years (range 31-84) and 65.3% were postmenopausal. A change of BC subtype was documented in 15/49 (30.6%) pts, with the higher rate in M1 group (52.4%); as opposed to the TN subset, a change to HER2+ disease was reported in 6/15 (40.0%) pts and just after the TN subtype in all cases. Family history of BC and/or ovarian cancer was reported in 42.9% pts and any genetic test to assess the hereditary risk was performed in 30.6% pts. Similarly to TN subset, lung (36.7%), lymph nodes and bone (34.7% each) and liver (24.5%) were the most frequent metastatic locations; central nervous system metastases were developed by 14.3% pts. Visceral involvement was present in 66.7% pts, being this rate lower in M1 compared to PT and PT/M1 groups. The most frequent 1st-line therapies were chemotherapy (CT) (44.9%) and CT/biological therapy (BT) (36.7%). Type of CT mainly included capecitabine (36.4%), taxanes (27.3%), eribulin (13.6%) and platinum-based combinations (13.6%). Most pts received CT as monotherapy (86.4%). Bevacizumab (BVZ) was the most frequent BT associated to CT (77.8%), mainly with capecitabine and/or paclitaxel (72.2%). Progressive disease to 1st-line therapy in the whole group was reported in 73.5% pts (higher than in TN subset), with a median time to progression (TTP) of 5.7 mo (range 1.7-15.0); PT was the group with a higher PD rate. A 2nd-line therapy was reported in 63.3% pts. Similarly to 1st-line setting, the most frequent 2nd-line therapies were CT (74.2%) and CT/BT (12.9%) (with BVZ in 75.0% pts). CT in monotherapy was reported in 69.6% pts (capecitabine 31.3%, eribulin 25.0%). Median duration of this line therapy was 3.0 mo (range 0.6-15.8), PD has been reported in 96.8% pts (similar between groups), and 3rd-line therapy in 25/49 (51.0%) pts.

Conclusions: In TN/HER2-low ABC pts, lung, lymph nodes and bone were the most frequent metastatic locations. As opposed to TN subset, HER2+ disease is part of the subtype changes reported. Although the main 1st- and 2nd-line therapies were CT and CT/BT, similarly to TN subset, the rate of pts with PD to 1st- and 2nd-line therapies is higher, and also those pts treated in the 3rd-line setting.

Citation Format: Carlos Jara, Isabel Álvarez, César A Rodríguez, Purificación Martínez, Raquel Andrés, Álvaro Rodríguez-Lescure, Diego Malón, Jose Luis Alonso, Encarna Adrover, María José Echarri, Mireia Margeli, Ariadna Tibau, Judith Ramírez, Silvia Antolín, Ruth Campo, Juan José Miralles, Susana Bezares, Federico Rojo, Sara López-Tarruella, Angel Guerrero-Zotano. Geicam/2014-03 (registem): A prospective registry of advanced breast cancer: A subset of triple negative breast cancer patients with her2 low expression [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS7-35.