September 2019

A 45-YEAR-OLD MALE WITH A RIGHT ANTERIOR THIGH MASS

Contributors: 

Timothy R. Wysozan, MD

PGY-2 Resident Physician, Anatomic Pathology and Clinical Pathology

Indiana University School of Medicine

Ahmed K. Alomari, FEL, MD

Assistant Professor of Clinical Pathology & Laboratory Medicine

Indiana University School of Medicine

Clinical history: The patient is a 45-year-old male with a history of dermatofibrosarcoma protuberans in the left shoulder with multiple recurrences approximately 20 years ago. He presented with an exquisitely tender, subcutaneous, 5.0 cm mass in the anterior thigh that was active on PET-CT. An excision was performed.

Gross Examination: The specimen consisted of an ellipse of skin with associated subcutaneous fat, with dimensions of 8.4 x 2.5 x 1.9 to 2.4 cm. Within the same container, there was an irregular, ragged, grey-yellow lobulated fibrofatty tissue fragment, with dimensions of 1.8 x 1.4 x 0.6 cm.

Microscopic examination and immunohistochemistry: Histological examination of the small detached fragment of tissue revealed a proliferation of monotonous cells with rounded and centrally placed nuclei and lightly eosinophilic cytoplasm. A small, distinct component demonstrated small cytomorphology with no significant mitotic activity; however, the bulk of the proliferation showed slightly larger cells with increased mitotic activity (up to 3 mitoses per high power field) (Figures 1-3). 

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Figure 1: Hypercellular proliferation of monotonous cells (Hematoxylin & Eosin stain, original magnification X40)

                                

Fig. 1

Figure 2: Small, monotonous-appearing cells with rounded and centrally placed nuclei and lightly eosinophilic cytoplasm (upper right). Note the abrupt transition between smaller and larger cell populations (lower left) (Hematoxylin & Eosin, original magnification X400)

   Fig.2

Figure 3: Monotonous, slightly enlarged cells with rounded and centrally placed nuclei with prominent nucleoli, lightly eosinophilic cytoplasm, and increased mitotic rate (Hematoxylin & Eosin stain, original magnification X400).

 Fig.3

No severe cytologic atypia, atypical mitotic figures, necrosis, or infiltrative growth pattern was noted, although the latter feature was difficult to assess, given the fragmented nature of the specimen. The lesional cells were strongly positive for SMA and calponin, and focally positive for collagen type IV (Figures 4-6). They were negative for AE1/3, CD31, and SOX-10 immunostains. 

Figure 4: Diffuse positive staining for SMA (original magnification X400)

Fig.4

Figure 5: Diffuse positive staining for calponin (original magnification X400)

Fig.5

Figure 6: Focal positive staining for collagen type IV (original magnification X400).

Fig. 6

September 2019 Final Diagnosis and Discussion