The clinical utility of neuron-specific enolase serum levels as a biomarker for Merkel cell carcinoma.

9570 Background: To date no adequate biomarker for Merkel Cell carcinoma (MCC) has been identified. The introduction of immunotherapy (IT) for metastatic MCC increases the need for a biomarker. Serum Neuron-specific enolase (NSE) has already been tested and is commonly used as a biomarker for several small cell malignancies. However, the role of NSE in MCC is still unclear. Aim: To investigate the role of NSE as a biomarker in MCC. Methods: A prospective cohort of MCC patients treated from 2016 to July 2018 was analyzed. Kaplan Meier curves with log rank test, Cox regression and mixed models were used to analyze NSE. A separate evaluation was performed for patients treated with IT. Results: A total of 78 patients (42 males, median age 71 years, stage I&II, III and IV MCC in 37(47%), 39(50%) and 2(3%) patients at time of diagnosis with 474 NSE levels (median 15 ; IQR 12,6-22 ng/ml were included. Baseline NSE (n=36) had no influence on survival or progression. During follow-up (FU) NSE levels correlated with tumorload (p=0,01) with increase of 15 ng/ml per class (no tumorload, localized MCC, nodal and distant metastases, respectively). NSE level during FU was able to detect progression (AUC 0,89). Several cut off values were evaluated. A NSE of 18,2 ng/ml was considered the most optimal level for clinical use (sensitivity 91%, specificity 78%, PPV 48%, NPV 98% to detect progression). During IT (n=16; 195 NSE values) all complete responders (n=7) had a normalized NSE (<18,2 ng/ml), all partial responders (n=3) had a decreasing NSE. In non-responders (n=6) all NSE levels remained elevated, one patient responded after switching to different IT with normalizing NSE values. Conclusions: NSE seems to be a valuable biomarker in MCC. NSE correlates with tumorload; is able to rule out progression and distinguishes responders from non-responders during IT.