Abstract P2-01-05: Sensitive blood-based monitoring of breast cancer

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Abstract Breast cancer is the leading cause of cancer in women worldwide. Although there have been significant advances in the clinical management of breast cancer over the past few decades, women continue to die from this disease. Current methods for detection and monitoring of breast cancer progression, metastasis, and late recurrences lack sensitivity and have not yet been proven to significantly extend overall survival. Current research is focused on identifying novel monitoring methods, with a particular focus on blood-based tumour markers. Monitoring of circulating tumor cells improves detection, but the methods are complex and not applicable to routine practice. A new more sensitive method based on detection of circulating cell free tumor DNA has shown to be more sensitive for women known to have late stage disease. This is a great advance but has not been shown to be a valuable prospective monitoring tool. Tumor derived exosomes (TEX) represent an alternative blood-based method. These are small membrane vesicles that are secreted into the blood and harbor a molecular signature that are directly representative of their 'parent cell'. Emerging evidence suggests that TEX are a veritable 'treasure chest' from which an abundance of stable biomarkers can be isolated and applied to disease monitoring. We hypothesized that: (1) TEX harbor patient-specific DNA mutations similar to those of the patient's tumor; and (2) determining the number and genomic profile of TEX has the capacity for earlier identification of recurrent or progressive disease. To investigate this in a pilot study, TEX were isolated from the plasma of breast cancer patients (n=11) by ultracentrifugation. Western blotting and electron microscopy were performed to validate TEX isolation. DNA was extracted from TEX, patient-matched breast tumor tissue and buccal swabs. Next generation sequencing was performed using the Ion Torrent platform and the Cancer Hotspot Panel v2 (Life Technologies). Despite the small cohort size, there was a statistically significant association (p=0.028) between exosome protein yield and clinical disease stage. TEX protein levels were higher among patients with axillary lymph node involvement (mean 4.8µg per µl of plasma) compared to those with localized disease (mean 3.5µg per µl of plasma). In keeping with other studies the TEX contained low levels of double-stranded DNA that spanned the majority of the genome. Validation of the variants detected in the TEX is currently underway to confirm whether exosomal DNA contains the same genetic variants present in the primary neoplastic tissue. The early detection of breast cancer recurrence and progression represents an unmet challenge that needs to be overcome. This study demonstrates that with continued exploration, TEX may represent a novel approach for disease monitoring that has the potential to improve clinical management and survival. Citation Format: Meehan K, Ruhen O, Myna K, Mirzai B, Erber W. Sensitive blood-based monitoring of breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-01-05.