This article is available in open access under Creative Common Attribution-Non-Commercial-No Derivatives 4.0 International (CC BY-NC-ND 4.0) license, allowing to download articles and share them with others as long as they credit the authors and the publisher, but without permission to change them in any way or use them commercially  388 Guidelines Beata Kos-Kudła et al. Guidelinespersons/year, with the primary lesion most frequently found in the small intestine (37.4%). Since 2000, rectal NENs have been diagnosed more frequently than small intestine NENs [2, 6-8]. The incidence of GEP-NETs in the USA, based on SEER data, was 3.56/100,000 persons/year. In Europe, the incidence of GEP-NETs is also increasing -from 1.33 to 2.33/100,000 persons/year; however, these data come from different registries and are mainly retrospective. Higher incidence is observed among men (5.35/100,000 persons/year) compared to women (4.76/100,000 persons/year) [1, 5-7]. The vast majority of NENs are sporadic, well-differentiated tumours. However, GEP-NETs originating from the pancreas, duodenum, stomach, and much less frequently, from the thymus and lungs sometimes constitute an element of multiple endocrine neoplasia type 1 (MEN-1) syndrome. Pancreatic neuroendocrine tumours (PanNETs) may also be associated with von Hippel-Lindau (VHL) syndrome, tuberous sclerosis complex (TSC), and neurofibromatosis (NF). In these congenital diseases, NETs can be multifocal and occur 10-20 years earlier than in sporadic cases. The frequency of the hereditary causes (MEN-1, VHL) is estimated at about 5%. Genome studies revealed the presence of germline mutations in, e.g., MUTYH, CHEK2, and BRCA2 and a propensity to PanNETs in approximately 17% of the studied population [1]. Diagnostics Biochemical diagnosticsBiochemical diagnostics of NENs involves the following: A. Non-specific markersThe most frequently used diagnostic method is determination of the chromogranin A (CgA) concentration in the serum (less frequently in the plasma) [1,8,9]. CgA is a relatively stable protein in blood. However, there are two different methods for determining the concentration of CgA: radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) in Neuroendocrine neoplasms (NENs) arise from the disseminated system of neuroendocrine cells and can occur in various parts of the body. However, they are most often found in the gastrointestinal tract and lungs. The term NENs includes both well-differentiated neuroendocrine tumours and neuroendocrine carcinomas (NECs), which account for 10-20% of all NENs. The following characteristics of NENs should be considered in the diagnostic and therapeutic process: proliferative activity, presence of somatostatin receptors (SSTRs), tumour growth rate, and extent of the neoplastic disease [1].

Excessive free iron and the associated oxidative damage are commonly related to carcinogenesis. Among the antioxidants known to protect against iron-induced oxidative abuse and carcinogenesis, melatonin and other indole compounds recently have received considerable attention. Indole-3-propionic acid (IPA), a deamination product of tryptophan, with a structure similar to that of melatonin, is present in biological fluids and is an effective free radical scavenger. The aim of the study was to examine the effect of IPA on experimentally induced oxidative changes in rat hepatic microsomal membranes. Microsomes were preincubated in presence of IPA (10, 3, 2, 1, 0.3, 0.1, 0.01 or 0.001 mM) and, then, incubated with FeCl(3) (0.2 mM), ADP (1.7 mM) and NADPH (0.2 mM) to induce oxidative damage. Alterations in membrane fluidity (the inverse of membrane rigidity) were estimated by fluorescence spectroscopy and lipid peroxidation by measuring concentrations of malondialdehyde+4-hydroxyalkenals (MDA+4-HDA). IPA, when used in concentrations of 10, 3 or 2 mM, increased membrane fluidity, although at these concentrations it did not influence lipid peroxidation significantly. The decrease in membrane fluidity due to Fe(3+) was completely prevented by preincubation in the presence of IPA at concentrations of 10, 3, 2 or 1 mM. The enhanced lipid peroxidation due to Fe(3+) was prevented by IPA only at the highest concentration (10 mM). It is concluded that Fe(3+)-induced rigidity and, to a lesser extent, lipid peroxidation in microsomal membranes may be reduced by IPA. However, IPA in high concentrations increase membrane fluidity. Besides melatonin, IPA may be used as a pharmacological agent to protect against iron-induced oxidative damage to membranes and, potentially, against carcinogenesis.

This article is available in open access under Creative Common Attribution-Non-Commercial-No Derivatives 4.0 International (CC BY-NC-ND 4.0) license, allowing to download articles and share them with others as long as they credit the authors and the publisher, but without permission to change them in any way or use them commercially gonoma -glucagon-producing tumour, VIPoma -vasoactive intestinal peptide (VIP) producing tumour, GHRHoma -growth hormone-releasing hormone (GHRH)-producing tumour, ACTHoma -adrenocorticotropin hormone (ACTH)-producing tumour,

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