January 2016 Case of the Month

41 year-old woman presents with a "left flank mass" per requisition, status post incisional biopsy.  What is your diagnosis?

2x
2x

Low power reveals a somewhat circumscribed tumor with dense eosinophilic appearance and peripheral rim of adjacent adipose.

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10x
10x

The tumor displays sweeping and haphazardly arranged fascicles of spindle cells with scattered thick and thin walled vessels and an entrapped nerve in the background.

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Beta Catenin 40x
Beta Catenin 40x

Positive both nuclear and cytoplasmic staining (the vascular endothelial nuclei serve as good negative internal controls)

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2x
2x

Low power reveals a somewhat circumscribed tumor with dense eosinophilic appearance and peripheral rim of adjacent adipose.

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January 2016 Case of the Month

   Answer: Deep Fibromatosis (Desmoid Tumor)

Deep fibromatosis or desmoid tumor is a fibroblastic/myofibroblastic neoplasm that typically arises in abdominal or extra-abdominal (limb girdle) musculoaponeurotic structures.  Intra-abdominal desmoid tumors usually arise in the mesentery, pelvis, or retroperitoneum, and some may be associated with Gardner syndrome (germline APC gene mutation).  Abdominal desmoids usually affect adult women (30-40 years) while extra and intra-abdominal tumors show equal sex predilection of young to middle aged adults.  Desmoid tumors are generally slowly growing, painless masses.  These tumors lack the capacity to metastasize, and have thus been historically considered to be benign tumors.  However, depending upon location these lesions may infiltrate into adjacent structures leading to morbidity.  By immunohistochemistry, these tumors show positivity for smooth muscle actin, varying desmin, and nuclear beta-catenin expression.  Treatment is centered around wide local excision.  These tumors have a tendency to recur if incompletely excised.  Radiation therapy may be indicated for some desmoid tumors.