To Örebro University

Introduction: There are only few studies on the diagnostic value of serum 5HIAA as compared to the 24-hours urinary sampling method and a lack of evidence on the prognostic significance of its serum levels, as well as the markers' ability to predict changes in disease status.

Aim(s): Our aim was to investigate the clinical utility of serum 5HIAA for diagnostic purposes and disease surveillance in a cohort of patients with well-differentiated neuroendocrine neoplasms (WD-NENs).

Materials and methods: Forty-eight patients with WD-NENs and concurrent serum and urinary 5HIAA testing as well as CT/MRI imaging were included.

Results: A positive correlation between disease stage and serum 5HIAA positivity (Pearson Chi-square p=0.017), and between liver tumor burden and serum 5HIAA levels (Spearman’s rank correlation coefficient: 0.46; p=0.013) was confirmed. Further analysis did not reveal any correlation between RECIST 1.1 responses and >25% changes in serum 5HIAA levels (Fisher ́s exact test p=0.735). The concordance rate of serum and urinary 5HIAA positivity at standardized laboratory cut-offs was 75%. In patients without any impairment of the renal function, the concordance between the two tests was as high as 89% and a sensitivity and specificity of 80% and 88.9%, respectively was evident (Cohen’s kappa coefficient=0.685).

Conclusion: Serum 5HIAA performs well compared to urinary testing for diagnostic purposes and corresponds well to tumor stage and liver tumor burden. However, it is not adequate to predict tumor progression.