EWSR1-SMAD3-positive fibroblastic tumor

Last revised by Reabal Najjar on 13 Nov 2022

EWSR1-SMAD3-positive fibroblastic tumors are benign mesenchymal neoplasms with different morphologies and a provisional name that have been just recently characterized (c.2018) 1-4 and added to the WHO classification of soft tissue tumors in 2020 2,3.

EWSR1-SMAD3-positive fibroblastic tumors are sporadic soft tissue neoplasms. They appear in a wide age range, with women more commonly affected than men 2.

The diagnosis of EWSR1-SMAD3-positive fibroblastic tumors is established by location, histological, immunohistochemical, and molecular criteria 1.

Diagnostic criteria according to the WHO classification of tumors: soft tissue and bone (5th edition) 2:

  • small acral tumors of the skin and subcutaneous tissue

  • a zonal pattern of a hyalinized acellular center and fascicular spindle cells in the periphery

  • immunoreactivity to ERG

The following diagnostic criterion is desirable 2:

  • EWSR1-SMAD3 fusion

EWSR1-SMAD3-positive fibroblastic tumors usually present as painless, small, superficial nodules in an acral location in the hands and/or feet 1,3.

EWSR1-SMAD3-positive fibroblastic tumors are characterized by a zonal morphology of intersecting cellular fascicles composed of monomorphic spindle cells and hypo to acellular hyalinised areas 1-4.

The etiology of those tumors is currently unknown 2.

EWSR1-SMAD3-positive fibroblastic tumors are most commonly located in the skin or the subcutaneous tissue of the hands and feet 1-4.

Tumors are characterized by a nodular appearance and are usually of small size (up to 1-2 cm) 1,2.

Histologically EWSR1-SMAD3-positive fibroblastic tumors display the following characteristics 1-4:

  • acellular hyalinized center

  • hypercellular peripheral zone with intersecting cellular fascicles of bland spindle cells

  • absence of nuclear pleomorphism, hyperchromasia and increased mitotic activity

  • possibly stippled dystrophic calcification

Immunohistochemistry stains show diffuse nuclear reactivity for ERG, but do not express CD34 or smooth muscle actin 1,2,4.

Those tumors are characterized by genetic EWSR1-SMAD3 fusions 1.

At the time of writing, there are only very few reports of the radiological features of this entity 5.

On ultrasound, the tumors have been characterized by hypoechoic subcutaneous nodules 5.

The tumor has been described as well-circumscribed small lesions 5.

  • T1: hypointense

  • T2: hyperintense

The radiological report should include a description of the following:

  • form, location, and size

  • tumor margins

  • relation to muscular fasciae

  • relationship to local nerves and vessels

The tumors are benign. Local recurrences are seen upon incomplete excision 1,2.

EWSR1-SMAD3-positive fibroblastic tumors have been first described by the Taiwanese pathologist Yu-Chien Kao and his American and Dutch colleagues Lei Zhang, Yun-Shao Sung, Albert JH Suurmeijer and Cristina R Antonescu 1.

Conditions that can mimic the presentation and/or the appearance of EWSR1-SMAD3-positive fibroblastic tumors include the following:

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