Fibromatosis – immunohistochemical evaluation, differential diagnosis from gastrointestinal tumors, and other mesenchymal tumours

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. b-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.