Elevated Serotonin and NT-proBNP Levels Predict and Detect Carcinoid Heart Disease in a Large Validation Study

SIMPLE SUMMARY: A relevant proportion of patients with neuroendocrine tumors (NET) develop carcinoid heart disease (CHD). This rare cardiac condition leads to worsened survival rates in patients with NET. In this study, we investigated various biomarkers in the blood that could detect and, more specifically, predict which patients are at high risk of developing CHD. In this large study of patients with CHD, we found two biomarkers, NT-proBNP and serotonin, that together are very useful in the prediction and detection of CHD. Moreover, we found cut-off values for NT-proBNP that will aid in the screening of patients with NET, thereby increasing focus on patients at high risk of developing CHD, and releasing patients with a low risk of CHD from burdening screening. ABSTRACT: Carcinoid heart disease (CHD) is a rare fibrotic cardiac complication of neuroendocrine tumors. Besides known biomarkers N-Terminal pro-B-type natriuretic peptide (NT-proBNP) and serotonin, activin A, connective tissue growth factor (CTGF), and soluble suppression of tumorigenicity 2 (sST2) have been suggested as potential biomarkers for CHD. Here, we validated the predictive/diagnostic value of these biomarkers in a case-control study of 114 patients between 1990 and 2021. Two time-points were analyzed: T(0): liver metastasis without CHD for all patients. T(1): confirmed CHD in cases (CHD+, n = 57); confirmed absence of CHD five or more years after liver metastasis in controls (CHD–, n = 57). Thirty-one (54%) and 25 (44%) females were included in CHD+ and CHD– patients, respectively. Median age was 57.9 years for CHD+ and 59.7 for CHD- patients (p = 0.290). At T(0): activin A was similar across both groups (p = 0.724); NT-proBNP was higher in CHD+ patients (17 vs. 6 pmol/L, p = 0.016), area under the curve (AUC) 0.84, and the most optimal cut-off at 6.5 pmol/L. At T(1): activin A was higher in CHD+ patients (0.65 vs. 0.38 ng/mL, p = 0.045), AUC 0.62, without an optimal cut-off value. NT-pro-BNP was higher in CHD+ patients (63 vs. 11 pmol/L, p < 0.001), AUC 0.89, with an optimal cut-off of 27 pmol/L. Serotonin (p = 0.345), sST2 (p = 0.867) and CTGF (p = 0.232) levels were similar across groups. This large validation study identified NT-proBNP as the superior biomarker for CHD. Patients with elevated serotonin levels and NT-proBNP levels between 6.5 and 27 pmol/L, and specifically >27 pmol/L, should be monitored closely for the development of CHD.