Abstract PS10-44: Termination of trastuzumab-based treatment after complete response in HER2-positive metastatic breast cancer
Authors: Dogan Izzet , Aydın Esra , Khanmammadov Nijat , Aydıner Adnan , Saip Pınar 
Published: February 2021

Abstract
Background: Trastuzumab has been used for HER2 positive breast cancer treatment for more than 20 years. The ratio of HER2 overexpression in breast cancer patients is about 20%. In this study, we aim to evaluate the prognosis of HER2 positive breast cancer patients with long term received trastuzumab and examined the predictors of complete response.
Method: In this study, we included the patients with HER2 positive metastatic breast cancer received long-term trastuzumab. Demographic, clinical, pathological, and treatment data of the patients retrospectively recorded. Response rates of trastuzumab-based treatment evaluated by RECIST. The prognosis of the patients and predictors of complete response assessed with Kaplan-Meier analysis and logistic regression analysis, respectively. Also, the prognosis of the patients whose trastuzumab-based treatment was terminated was evaluated.
Results: Median follow-up was 123.3 months (range, 32.2-330.3). Eighty patients included the study, and the median age of the patients was 43 (22-68). The patients received trastuzumab-based treatment with a median of 62 months (range, 12-191). The number of de-novo metastatic patients was 27 (33.8%). All patients had a pathological HER2 overexpressed tumor that scored 3+ (71.3%) by ımmunohistochemistry (IHC) or scored 2+ (28.7%) by IHC confirmed with FISH. In all patients, five-, ten-, and, fifteen – years overall survival were 96.1%, 86.8%, and 60.5%, respectively. A complete response was detected at 60 (75%) of the patients. The median time to complete response was 14.4 months (range, 2.4-47.8). In logistic-regression analysis: age at diagnosis (p=0.543), menopausal status (p=0.074), bisphosphonates treatment (p=0.682), palliative radiotherapy (p=0.935), and de-novo metastatic disease (p=0.405) were not statistically significant predictors for complete response. However, the number of metastatic sites (p=0.016), and the use of endocrine therapy (p=0.019) with trastuzumab were statistically significant. During the study period, trastuzumab-based treatment of twelve patients was terminated, four (33.3%) patients continue to receive aromatase inhibitör, and eight (66.7%) patients received no treatment. After termination of trastuzumab, at a median follow-up 44.7 months (range, 11.6-66.6), recurrence was not detected in the patients.
Conclusions: In this study, we found that trastuzumab-based therapy can provide full recovery of HER2 positive metastatic breast cancer. For the patients with a long-term complete response, discontinuation of trastuzumab-based treatment should be considered. Also, hormone-positive patients should continue to receive aromatase inhibitör. The use of endocrine therapy with trastuzumab and the number of metastatic sites are predictors of the complete response
Citation Format: Izzet Dogan, Esra Aydın, Nijat Khanmammadov, Adnan Aydıner, Pınar Saip. Termination of trastuzumab-based treatment after complete response in HER2-positive metastatic breast cancer [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 PS10-44.