Abstract P3-02-06: Demographic and clinical features of patients with metastatic HER2 positive breast cancer: a retrospective multicenter registry study of the Turkish Oncology Group
Authors: ERALP Yeşim , DOĞAN İzzet , Aksoy Sercan , ÇAKAR Burcu , BAŞARAN Gül , ERCELEP Özlem , MANDEL Nil MOLİNAS , KORKMAZ Taner , GÖKMEN Erhan , AYDINER Adnan , SAİP Pınar 
Published: March 2023

Background: Although HER2 is an aggressive subtype of BC, the outcomes have improved over the past two decades due to advances in targeted therapies. Here, we present data of HER2-positive subset from the multicenter registry study of the Turkish Oncology Group (TOG) for metastatic breast cancer with an evolving treatment landscape for over a decade (MBC). Methods: The study of TOG for MBC was a retrospective registry study aimed to collect the data of adult metastatic BC patients diagnosed between 2010-2019, at seven tertiary oncology clinics in Turkey. Patient and disease characteristics were recorded from chart reviews. HER2 (+) was defined as IHC scores of IHC3+ or IHC2+ and ISH (+). Overall survival (OS) and progression-free survival (PFS) were calculated by the Kaplan-Meier method. Correlations between demographic, prognostic variables and survival outcomes were carried out in database aggregates comprising of cohorts based on disease presentation (recurrent vs de-novo) and the diagnosis date of MBC (Cohort I: patient diagnosed between January 2010-December 2014 and Cohort II: between January 2015-December 2019). Results: Of the 1381 patients analyzed over the whole period, 333 (24.1%) HER2 (+) MBC patients were identified. 55.0% of the patients were in Cohort I. The majority (56.8%) had de novo MBC. Despite a decreasing frequency over time (63.4% in Cohort I vs 48.7% in Cohort II, p=0.007), this was the largest group with among all pathological subgroups presenting with de novo disease. 17 patients (2.4% of recurrent patients) demonstrated changes in HER2 receptor status from negative to positive between the primary tumor and subsequent metastasis. Recurrent BC patients were significantly younger than de novo MBC patients [44 (22-80) years vs 49 (20-91) years, p=0.006] and 43.1% (n=62) had relapsed within two years from initial diagnosis. Recurrent BC patients showed a higher frequency of brain metastasis as compared to de novo patients (13.2% vs 1.1%), whereas non-CNS visceral organ metastases were more common in de novo MBC patients (58.7% vs 47.9%, respectively, p&lt; 0.001). Following conditional approval of use in de novo visceral metastatic disease in 2016, dual-HER2 blockade including pertuzumab was more frequently used in Cohort II compared to Cohort I (p&lt; 0.001). Although overall median PFS was not statistically significant between the two cohorts (Cohort II vs I; 22 vs 17 months, respectively, p=0.609), there was a significantly higher PFS in the de novo group in Cohort II (29 vs 17 months, p=0.037). Furthermore, there was a significant improvement in median OS in Cohort II compared to Cohort I [not reached vs 48.0 (40.0-71.0) months, respectively; p=0.017]; mainly driven by the de novo group in alignment with the approval indication for dual blockade (Cohort I vs II; 3-year OS; 62.0% vs 84.7%; p=0.009); especially those with visceral metastatic presentation (59.4% vs 83.4%, p=0.020); HR (+) HER2 (+) disease (61.2% vs 89.2%; p=0.013) and age&lt; 40 years (40.0% vs 94.7%; p=0.009). Conclusion: There was a significant survival benefit achieved in patients with metastatic HER2 (+) disease over time, regardless of high-risk factors such as visceral involvement or young age, mirroring advances in the timeline of anti-HER2 treatment.

Citation Format: Yeşim ERALP, İzzet DOĞAN, Sercan Aksoy, Burcu ÇAKAR, Gül BAŞARAN, Özlem ERCELEP, Nil MOLİNAS MANDEL, Taner KORKMAZ, Erhan GÖKMEN, Adnan AYDINER, Pınar SAİP. Demographic and clinical features of patients with metastatic HER2 positive breast cancer: a retrospective multicenter registry study of the Turkish Oncology Group [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 P3-02-06.