Trends in the management of small HER2-positive breast cancers.

person Carolin Mueller Outcomes Research Consortium, Department of Anesthesiology, Cleveland Clinic Foundation, Cleveland, OH info_outline Carolin Mueller, Rangan Rahul, Megan Lynn Kruse, Zahraa Alhilli

Authors person Carolin Mueller Outcomes Research Consortium, Department of Anesthesiology, Cleveland Clinic Foundation, Cleveland, OH info_outline Carolin Mueller, Rangan Rahul, Megan Lynn Kruse, Zahraa Alhilli Organizations Outcomes Research Consortium, Department of Anesthesiology, Cleveland Clinic Foundation, Cleveland, OH, Breast Center, Integrated Surgical Institute, Cleveland Clinic Foundation, Cleveland, OH, Department of Hematology/Oncology, Cleveland Clinic Foundation, Cleveland, OH Abstract Disclosures Research Funding No funding sources reported Background: Small HER2 positive breast cancers have not been well studied in randomized trials. The treatment landscape for this population aims to optimize efficacy while minimizing potential over-treatment and associated toxicities. Due to the potential for post-neoadjuvant therapy optimization, use of neoadjuvant systemic therapy (NAT) increased in recent years. However, this approach can often lead to overtreatment of patients with small tumors. This study aims to evaluate recent trends in treatment patterns of patients with T1 HER2 positive tumors. Methods: Patients diagnosed with HER2 positive, T1, any N, breast cancer treated at a single institution from January 2018 to December 2022 were included. Clinicopathological data, treatment data, and survival data were collected and analyzed. Results: 326 patients were included. Mean age was 62 (±12.2) years. T category included 3 (0.9%) cT0, 17 (5.2%) cTmi, 28 (8.6%) cT1a, 94 (28.8%) cT1b, 178 (54.6%) cT1c tumors, and 6 patients (1.8%) had clinical T1 stage without further specification. 41 patients (12.6%) had cN+ disease and 243 (74.5%) were hormone receptor positive. Systemic therapy data was available for 288 patients; 7 (2.4%) received Herceptin monotherapy, 105 (36.5%) Taxol + Herceptin, 41 (14.2%) Taxol + Carboplatin + Herceptin, and 74 (25.7%) Taxol + Carboplatin + Herceptin + Pertuzumab (TCHP), 12 (4.2%) other. 49 patients (17%) did not receive any systemic therapy. 58 patients (17.8%) were treated with NAT and a pathologic complete response rate was noted in 39 patients (67.2%) undergoing NAT. Overall, in patients who received systemic therapy, NAT increased from 2018 (17.6%) to 2021 (37.5%) and decreased in 2022 (23.5%). Similar patterns were observed in patients with T1a/b (2021: 17.4%; 2022: 0%), as well as T1c (2021: 51.4%; 2022: 36.4%). TCHP was the most commonly administered NAT regimen (86.2%). Discontinuation or dose reduction occurred in a total of 57 patients (18.8%). Conclusions: The primary treatment for T1 HER2 positive breast cancers is surgery with adjuvant HER2 targeted therapy in combination with chemotherapy. Although NAT witnessed an upward trend from 2018 to its peak in 2021, its utilization declined again in 2022. A balance between the most effective treatment and minimizing toxicities should be ensured.