Introduction. The identification of the type and site of origin in undifferentiated tumours of unknown primary site using immunohistochemistry is a frequent requirement in pathology practice. There are many histologic lesions that display similar morphologic aspects, with misdiagnosis potentially resulting in over- or undertreatment. This makes the diagnostic accuracy extremely important in the era of targeted therapies.
The objective of the study was to evaluate the process of diagnosis in 50 melanoma cases presenting as poorly differentiated or undifferentiated tumours with unknown primary origin, with emphasis on the immunohistochemical algorithm.
Methods. 50 cases were selected to analyse the utility of IHC testing in diagnosing poorly differentiated malignancies. The immunohistochemical evaluation was based on the staining percentage of cells: focal positive <50%, diffuse positive >50%, negative (-) 0%.
Results. After applying the Fan Lin algorithm, for most of the cases (45), the cytokeratin and CD45 proved negative, while S100 and vimentin were positive in diffuse or zonal patterns. For the 3 cases analysed by applying the Turin algorithm, the first antibody panel consisted in testing CK7/CK20, that showed no expression for all 3 cases.
Conclusions. In this study, we demonstrated that the immunohistochemical examination of poorly differentiated malignant tumours is a reliable and valuable test and is recommended as a standard method in diagnosis along with the correlations with clinical and histological data.
Keywords: metastatic melanoma, undifferentiated tumour, immunohistochemistry algorithm.
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