Introduction: The biochemical diagnosis of neuroendocrine tumours (NETs) uses assays of specific and nonspecific markers. Nonspecific markers include, among others, neuron-specific enolase (NSE). The aim of this study was to evaluate NSE in patients with midgut type tumours treated with somatostatin analogues.

Material and methods: The study group of patients with NETs of the small intestine included 41 patients. Grade G1 was found in 19 cases, while G2 was seen in the remaining 22 cases. Liver metastases were found in all patients studied. The examined group of patients was treated with somatostatin analogues receiving octreotide LAR at a dose of 30 mg. The control of biochemical parameters was performed every 3 months and imaging examinations every 6 months. The Immuno-Biological Laboratories kit was used for determination of NSE concentration, where reference values were 12.5–25 ng/mL.

Results: In the G1 group of patients, the median value of NSE concentration was 134.67 ng/mL, while in the G2 group, the value was 234.55 ng/mL and was significantly higher than in the G1 group (p = 0.003). In the determination of NSE concentration values according to the degree of liver involvement, in the group of patients with 10% liver involvement, the median value of NSE concentration was 143.21 ng/mL, while in the group with 25% liver involvement, the value was 251.82 ng/mL (p < 0.001). In the analysis of NSE concentration assessment in patients with disease progression, the median value was 234.65 ng/mL compared to the group with disease stabilization, where the median NSE value was significantly lower and amounted to 136.27 ng/mL (p < 0.001).

Conclusions: In our study, we observed that NSE concentration values were significantly higher among patients with NET midgut type tumour with histological grade G2 and in patients with 25% liver involvement and progression of the disease process.