An epithelioid enigma

 
Image 1:  Low power magnification of a sharply demarcated cellular proliferation.

Image 1:  Low power magnification of a sharply demarcated cellular proliferation.

Image 2: Higher magnification showing spindled and epitheliod cells that are uniform, without cytologic atypia or mitotic figures.  An Immunohistochemical panel using antibodies to various cytokeratins was negative.

Image 2: Higher magnification showing spindled and epitheliod cells that are uniform, without cytologic atypia or mitotic figures.  An Immunohistochemical panel using antibodies to various cytokeratins was negative.

Image 3:  Smooth muscle actin highlights the cellular proliferation.

Image 3:  Smooth muscle actin highlights the cellular proliferation.

Image 4:  The cellular proliferation also expresses CD34.

Image 4:  The cellular proliferation also expresses CD34.

DIAGNOSIS:  Epithelioid myofibroblastoma

DISCUSSION:  Myofibrobastoma is a benign lesion that is part of the spectrum of spindle cell lipoma.  The lesion is composed of myofibroblasts, which may range from spindle cells resembling a schwannoma, to epithelioid cells which mimic a carcinoma.  The epithelioid variant may be mistaken for an invasive lobular carcinoma, and the expression of estrogen receptor by myofibroblastoma can be further confusing.  However, lack of cytokeratin expression excludes carcinoma.  Myofibroblastomas characteristically express CD34 and usually express desmin and smooth muscle actin.