Abstract P4-21-36: Splenic enlargement and bone marrow hyperplasia in patients receiving trastuzumab-emtansine for metastatic breast cancer

Abstract

Abstract Introduction Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate used for treatment of human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer. An association between T-DM1 and splenic enlargement was noted anecdotally on sequential whole-body MRI (WB-MRI) examinations. A retrospective analysis of WB-MRI examinations of patients on T-DM1 was undertaken to investigate the hypothesis that an increase in splenic volume is due to either a generalised hyperplasia of the bone marrow and reticulo-endothelial system and/or an increase in portal venous pressure. Methods 12 patients underwent 29 serial WB-MRIs before and during T-DM1 therapy. Splenic volume, portal vein diameter, bone marrow muscle-normalised signal intensity (nSI), water diffusivity (apparent diffusion coefficient, ADC) and fat fraction were measured. Changes in splenic volume were analysed, and correlations between the measured variables were obtained. Results An increase in splenic volume was observed in 92% of patients. Mean splenic volume increased from 144cm3 (95%CI 110-177cm3) to 209cm3 (95%CI 161-257cm3) on T-DM1 therapy (p=0.006). Increase in splenic volume correlated with treatment duration (r2=0.71). Increase in normal bone marrow signal was seen (nSI 3.5 to 4.8, p=0.12), along with a decrease in fat fraction (64.3% to 57.3%, p=0.12), and reduced ADC (655µm2/s to 543µm2/s, p=0.11). No consistent changes to portal vein diameter were seen. Discussion An increase in splenic volume was consistently observed in patients on T-DM1 therapy. This was unrelated to portal vein changes but correlated with bone marrow hyperplasia. Caution should be applied when assessing metastatic disease in bone to avoid incorrectly attributing T-DM1-related changes in normal bone marrow to disease progression. Citation Format: Kosmin M, Makris A, Jawad N, Miles D, Padhani AR. Splenic enlargement and bone marrow hyperplasia in patients receiving trastuzumab-emtansine for metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-21-36.