Abstract PS6-48: Clinicopathologic features and follow-up outcomes of breast cancers with HER2 FISH group 3 Results: A single institution experience

Abstract

Abstract INTRODUCTION: There is dearth information on the long-term outcome and role of HER2 targeted therapy in breast cancer patients in the HER2 FISH group 3 category, which is defined as breast cancer with a HER2/CEP17 ratio < 2 and HER2 copy number ≥ 6 signals/cell. In this study, we report the clinicopathologic features and outcomes of breast cancer patients in the HER2 FISH group 3 category at our institution. METHODS: We identified 52/2,874 (1.8%) breast cancer patients with HER2 FISH group 3 results between 1/2007 and 3/2020. 28 of these 52 patients had available detailed clinicopathologic and follow-up data, with an average follow-up of 38.5 months. RESULTS: Most of the cases with group 3 FISH results were high grade ductal carcinomas with positive hormonal receptor expressions and equivocal HER2 expression by immunohistochemistry. Among all the clinicopathologic variables, only tumor size (p=0.048) significantly contributed to the poor clinical outcomes. HER2 copy number failed to show any significant association with histologic grade, tumor size, clinical stage, hormonal receptor status or disease outcomes. There was no statistically significant difference in disease outcome between patients who were treated with HER2 targeted therapy and patients who did not receive HER2 targeted therapy, regardless of the HER2 copy number or clinical stage (Table 1). CONCLUSION: Our preliminary findings suggest that certain patients with HER2 FISH group 3 category breast cancer may not need HER-2 targeted therapy. Larger-scale studies are needed to further evaluate which HER2 FISH group 3 results are more likely to benefit from the HER-2 targeted therapy. Table 1. Response to HER2 targeted therapy in HER2 FISH group 3 breast cancer patients based on HER2 copy numbers and clinical stageHER 2 targeted therapyp-valueGivenNot givenTotal populationGood outcome (n=21)1380.371Bad outcome (n=7)61HER2 copy number < 10Good outcome (n=16)1060.366Bad outcome (n=7)61HER2 copy number ≥ 10Good outcome (n=5)321.000Bad outcome (n=0)00Stage I-IIGood outcome (n=16)970.737Bad outcome (n=3)21Stage III-IVGood outcome (n=5)410.343Bad outcome (n=4)40*Good outcome = No evidence of disease**Bad outcome = Local recurrence, distant metastasis, and/or died of disease Citation Format: Huina Zhang, Rana Ajabnoor, David Hicks, Bradley Turner. Clinicopathologic features and follow-up outcomes of breast cancers with HER2 FISH group 3 Results: A single institution experience [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 PS6-48.