Large right temporal mass in young adolescent

A 16-year-old White woman presented with a facial lesion on the right side (Fig 1) that rapidly enlarged over 3 months. Patient denies previous trauma and personal or family history of melanoma. Physical examination revealed a well-circumscribed right temporal mass with a base measuring approximately 2 cm. No palpable lymphadenopathy of cervical, submandibular, or submental clusters were noted. The excisional biopsy sample stained with hematoxylin and eosin (Fig 2, A) revealed ulcerated skin with underlying inflammation and benign vascular proliferation with a variety of patterns; there were clusters of spindle cells and small capillary vessels to large dilated vessels. Biopsy sample stained with smooth muscle actin (SMA) demonstrated positive in vessels and stroma (Fig 2, B).

Fig 1.

Fig 2.

Question 1: Considering the clinical and histopathologic images, what is the most likely diagnosis?

• A.Dermatofibrosarcoma protuberans
• B.Nodular fasciitis
• C.Keloid
• D.Desmoid tumor
• E.Proliferative myositis

Answers:

• A.Dermatofibrosarcoma protuberans – Incorrect. Dermatofibrosarcoma protuberans is a locally aggressive tumor of fibroblastic origin. The initial lesion is a skin-colored plaque that develops a red/brown color and a nodular surface.¹ The lesion grows slowly and its histology shows storiform islands of bland spindle cells and the diffused expression of CD34 immunohistochemically.¹
• B.Nodular fasciitis – Correct. Nodular fasciitis usually manifests as a rapid growing, well-defined, benign, self-limiting soft-tissue lesion, which tends to be <4 cm. It is most commonly observed in the upper extremities, particularly the forearm, followed by the trunk, lower extremity, and head and neck region. The benign proliferation of fibroblasts and myofibroblasts are typically mistaken for a sarcomatous lesion because of its rapid growth, abundant spindle-shaped cells, and mitotic activity.^2,3
• C.Keloid – Incorrect. Keloid is a benign, firm, smooth, hard growth caused by a spontaneous, exaggerated fibroblast reaction to injury—often in the earlobe.⁴ Histology shows numerous fibroblasts and keloidal collagen, which are large, abnormal, hyalinized bundles of collagen.⁴
• D.Desmoid tumor – Incorrect. Desmoid tumor (fibromatosis) is a benign but locally aggressive neoplasm. Most affected sites include the mandible, submandibular area, neck, and tongue.³ Histology shows bland spindles cells invading muscles and other normal tissues.³
• E.Proliferative myositis – Incorrect. Proliferative myositis is an infiltrative, poorly demarcated intramuscular mass. Although it is similar to nodular fasciitis, it is characterized by large basophilic cells resembling ganglion cells. Histology shows ganglion-like cells and no damage to muscle fibers. The result is a checkerboard pattern with lesional cells between patches of intact muscle.²

Question 2: Which of the following histologic findings would be expected with this diagnosis?

• A.Variably myxoid to collagenous stroma, with scattered lymphocytes and extravasated erythrocytes. Histology is positive for SMA, muscle specific actin, and calponin and negative for desmin and S100.
• B.Consists of spindle-shaped cells that stain positive for SMA and ganglion-like myofibroblasts that stain negative for SMA.
• C.Wide bands of collagen with large, brightly eosinophilic glassy fibers with parallel fibroblasts and myofibroblasts on the basis of histology.
• D.Dense, storiform cell clusters entrapped in adipose tissue with minimally pleomorphic spindle cells and immunohistochemical staining positive for CD34.
• E.Immunohistochemical staining revealed positive results for desmin, actin, and B-catenin.

Answers:

• A.Variably myxoid to collagenous stroma, with scattered lymphocytes and extravasated erythrocytes. Histology is positive for SMA, muscle specific actin, and calponin and negative for desmin and S100 – Correct. This is a spindle stellate cell neoplasm arranged in short bundles and fascicles with a loose fascicular to storiform pattern (“feathery” growth). The nuclei are ovoid and monomorphic, with occasional mitotic activity.^2,3
• B.Consists of spindle-shaped cells that stain positive for SMA and ganglion-like myofibroblasts that stain negative for SMA – Incorrect. While nodular fasciitis closely resembles proliferative myositis, the latter includes the presence of ganglion-like myofibroblasts with vesicular nuclei and basophilic cytoplasm.²
• C.Wide bands of collagen with large, brightly eosinophilic glassy fibers with parallel fibroblasts and myofibroblasts on the basis of histology – Incorrect. The histologic hallmark of a keloid is increased whorls of thickened, hyalinized collagen bundles widely known as keloidal collagen.⁴
• D.Dense, storiform cell clusters entrapped in adipose tissue with minimally pleomorphic spindle cells and immunohistochemical staining positive for CD34 – Incorrect. Dermatofibrosarcoma protuberans is a rare and poorly circumscribed soft-tissue tumor that typically involves the dermis and subcutis. Unlike dermatofibrosarcoma protuberans, nodular fasciitis is typically negative for CD34.¹
• E.Immunohistochemical staining revealed positive results for desmin, actin, and B-catenin – Incorrect. Biopsy of desmoid tumors would show spindle and rhabdoid cells with mitotic figures staining positive for desmin, actin, and B-catenin.³

Question 3: The presence of which of the following fusion genes can be used to support this diagnosis?

• A. COL1A1-PDGFB
• B. FUS-DDIT3
• C. EWSR1-FLI1
• D. MYB-NFIB
• E. MYH9-USP6

Answers:

• A.COL1A1-PDGFB – Incorrect. The fusion product of COL1A1-PDGFB is present in most cases of dermatofibrosarcoma protuberans.¹
• B.FUS-DDIT3 – Incorrect. The fusion product of FUS-DDIT3 is present in myxoid liposarcoma.⁵
• C.EWSR1-FLI1 – Incorrect. The fusion product of EWSR1-FLI1 is present in Ewing sarcoma.⁵
• D.MYB-NFIB – Incorrect. The fusion product of MYB-NFIB is present in adenoid cystic carcinoma.⁵
• E.MYH9-USP6 – Correct. The majority of nodular fasciitis cases contain MYH9-USP6 fusion genes. USP6 rearrangement can be established by fluorescent in situ hybridization, polymerase chain reaction, or next generation sequencing techniques.⁵

Conflicts of interest

None disclosed.