Introduction: Fibromatosis is a histologically benign growth of fibroblastic and myofibroblastic cells, with a potential to recur and invade local organs. It can occur as a superficial or deep form. Visceral fibromatosis and superficial fibromatosis are histologically similar. They both have alterations in the WNT signalling pathway, but mutations in the APC or β-catenin gene do not occur in superficial fibromatoses.
Aim: To present four cases of deep fibromatosis and one case of Peyronie's disease, along with immunohistochemical staining analysis and the criteria for differential diagnosis.
Material and methods: All patients were hospitalised in the Central Clinical Hospital of the MSWiA in Warsaw during the period of 2012-2015. Surgical specimens were examined, and tissue samples were embedded in paraffin blocks.
Results: As the result of the study we present a short algorithm of immunostainings that can be useful in differential diagnosis. When a spindle cell tumour is encountered in the abdomen a gastrointestinal stromal tumor (GIST) should always be excluded; therefore, a CD117 staining is recommended as the first step. When the staining is negative, fibromatosis can be taken into consideration. β-Catenin staining should be done in order to confirm that diagnosis.
Conclusions: The diagnosis of fibromatosis is not always simple; GISTs can easily be mistaken for it. Immunohistochemical staining with CD34 and CD117 antibodies are useful in differential diagnosis. DTF should present negative stainings for S100, CD34, CD99, and bcl-2, which can help to distinguish it from other mesenchymal tumours.
Keywords: desmoid; fibromatosis; gastrointestinal stromal tumor; immunostainings; β-catenin.