Exosomal Del-1 as a potent diagnostic marker for breast cancer: A prospective cohort study.

11548 Background: The authors recently reported exosomal Del-1 as a diagnostic marker for breast cancer (Moon PG et al, Clin Cancer Res. 2016). Therefore, the current study aimed to confirm the diagnostic role of exosomal Del-1 in a prospective cohort with breast cancer by comparing plasma exosomal Del-1 levels before and after curative surgery. Methods: To identify the optimal time of sampling after surgery, blood samples were serially collected at day 1, 3, 5, and 7 after surgery from 22 patients with breast cancer. Thereafter, one hundred fourteen breast cancer patients who underwent curative surgery were prospectively enrolled and then their exosomal Del-1 levels before and after surgery were compared using ELISA with both anti-Del-1 and anti-CD63 antibodies. Results: Among 22 patients for identifying the optimal sampling time, all the exosomal Del-1 levels were normalized at post-operative day (POD) 1 (0.5 or less), and therefore POD 3 or later was accepted for the sampling time for 114 prospective patient cohort.At diagnosis, exosomal Del-1 levels of 110 (96.5%) patients were higher ( > 0.5) and 109 (99.1%) patients showed a normalization of Del-1 after surgery including four patients with the borderline Del-1 (between 0.4 and 0.5). During the mean follow-up duration of 21.8 (range, 5.9 – 58.4) months, nine (7.9%) patients experienced relapses (4 loco-regional and 5 distant), where 3 out of 6 in high group ( > 0.5), 2 out of 4 in borderline group, and 4 out of 105 in normalized group (≤0.4). In particular, patients who relapsed in higher Del-1 group showed earlier relapse compared to the relapsed patients in lower Del-1 group. Conclusions: As the current prospective cohort study demonstrated a normalization of exosomal Del-1 after curative surgery, exosomal Del-1 can be confirmed as a potent diagnostic biomarker for breast cancer. Plus, a high Del-1 level after surgery seems related with early relapse suggesting a potential prognostic marker by identifying the existence of residual tumor.