BACKGROUND : 4D Ultrasound technology merging the Power Doppler option called High-Definition Flow (HDF) with Spatio-Temporal Image Correlation (STIC) is used in gynaecology and obstetrics. It seems to be a promising tool in assessing tissue vascularisation. The aim of the paper was to assess whether HDF STIC technique could be a useful tool for the evaluation of gastro-entero-pancreatic neuroendocrine neoplasm (GEP-NEN) advancement. METHODS : Forty-eight patients [mean age 57.7 ± 10.3 years; male 40.9% (n = 18)] diagnosed with metastatic GEP-NENs were included in the analysis. All subjects were enrolled in the Department of Endocrinology and Neuroendocrine Tumours, Medical University of Silesia, Katowice. We analysed liver metastases. Patients with G3 grading or faintly vascularised lesions were excluded. HDF STIC volumes were acquired during USG examination. 4D indices [volumetric pulsatility index (vPI) and volumetric systolic/diastolic index (vS/D)] were calculated using dedicated software. RESULTS : There were no correlations between vS/D and Ki-67 [p = 0.67; r = -0.19; (-0.28-0.19)], CgA [p = 0.47; r = -0.11; (-0.38-0,19)], 5-HIAA [p = 0.52; r = -0.09 (-0.37-0.2)], serotonin [p = 0.83; r = -0.03 (-0.32-0.26)], and VCAM-1 (p = 0.62; r = 0.09 (-03-0.47)]. The were no correlations between vPI and Ki-67 [p = 0.29; r = -0.16 (-0.45-0.14)], CgA (p = 0.46; r = -0.11 (-0.39-0.19)], 5-HIAA [p = 0.52; r = -0.09 (-0.37-0.2)], serotonin [p = 0.82; r = -0.03 (-0.32-0.26)], and VCAM-1 (p = 0.62; r = -0.09 (-03-0.47)]. There was no significant difference between carcinoid versus non-carcinoid patients if compared by vS/D and vPI (p = 0.62, p = 0.61, respectively). CONCLUSIONS : HDF STIC seems not to be an efficient marker to assess advancement of NENs, due to lack of correlation with widely used and approved markers of progression.