The aim of the study was to investigate specific clinical and morphological characteristics in biopsy specimens of the stomach and duodenum using immunohistochemical typing.Material and methods. Biopsy specimens – 19 from the stomach and 22 from the duodenum were examined. The specimens were obtained from 27 patients with later pathomorphologically verified amyloidosis. The specimens were fixed in 10% formalin solution, processed with the standard technique of histological tissue making and

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... dded into paraffin blocks. The tissue sections were stained with H&E and congo red. A broad panel of antibodies to different types of amyloidosis was used for immunohistochemical typing of amyloid deposits.Results. In total, 41 biopsy specimen of the gastric and duodenal amyloidosis was examined. Histological findings included interstitial and vascular amyloid deposits in stomach and duodenum. Based on the results of immunohistochemical typing of 19 gastric biopsy specimens, ALλ amyloidosis was found in 7 cases, AAamyloidosis – in 6, ALλ amyloidosis and transthyretin amyloidosis – in 2 cases each, and mixed type – in 2 biopsy specimens. Among biopsy specimens of the duodenum, ALκ – amyloidosis was diagnosed in 10 cases, AAamyloidosis – in 5, ALλ amyloidosis – in 4, transthyretin amyloidosis – in 2, and mixed type – in one biopsy specimen.Conclusion. Based on the study results, ALκ- and AA-amyloidosis were the most frequent amyloidosis types in the gastric and duodenal biopsy specimens. Immunohistochemical typing was successful in all cases, thus proving that the selected method was adequate for amyloidosis diagnostics.