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Superficial CD34-Positive Fibroblastic Tumour

Superficial CD34-positive fibroblastic tumor is a distinctive low-grade neoplasm of the skin and subcutis, characterized by a fascicular to sheet-like proliferation of spindled cells with abundant, eosinophilic, granular to glassy cytoplasm, marked nuclear pleomorphism, a low mitotic count, diffuse CD34 expression, and frequent aberrant keratin immunoreactivity.

Symptoms & Causes

Introduction

Superficial CD34-positive fibroblastic tumor is a low-grade skin and subcutis neoplasm marked by spindled cells with distinctive cytoplasm and nuclear features, expressing CD34 and often keratin.

Reference
WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [cited 2024 09 11]. (WHO classification of tumours series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/33.

Related Terminology
Acceptable: PRDM10-rearranged soft tissue tumor.

Subtype(s)
None

Symptoms

This tumor typically presents as a slow-growing, painless mass of the superficial soft tissues. A long pre-biopsy duration (> 5 years) is often noted.

Localization

This tumor most frequently occurs in the lower extremities, especially thigh, followed by arm, buttock, shoulder, and (rarely) vulva. tumor size varies from 1.5 to 10 cm but is usually < 5 cm.

Epidemiology

Fewer than 40 cases have been reported. Most have occurred in middle-aged adults (median age: 37 years), with a slight male predominance.

Etiology

Unknown

Diagnosis & Treatment

Staging

Not clinically relevant

Pathogenesis

PRDM10 rearrangements have been reported in 3 cases previously classified as superficial CD34-positive fibroblastic tumor.

Macroscopic Appearance

The tumors are circumscribed, firm, yellow to tan soft tissue masses with a variably gelatinous appearance.

Histopathology

The lesions grow in a relatively circumscribed, but at least partially infiltrative, fashion and are composed of highly cellular fascicles and sheets of spindled to epithelioid cells with abundant eosinophilic cytoplasm, often having a granular or glassy appearance. Lipidized tumor cells are commonly present. The neoplastic cells show moderate to marked nuclear pleomorphism, often with bizarre, hyperchromatic nuclei containing prominent nucleoli and intranuclear cytoplasmic pseudoinclusions. Despite these alarming nuclear features, mitotic activity is very low and necrosis is rarely seen. A mixed inflammatory cell infiltrate is often present. There is morphological overlap with tumors reported as PRDM10-rearranged soft tissue tumors. By immunohistochemistry, superficial CD34-positive fibroblastic tumors invariably express CD34 and are focally immunoreactive for keratins in close to 70% of cases (most often with the AE1/AE3 clones).

Cytology

Cytology shows cellular smears composed of large, pleomorphic cells with granular to glassy cytoplasm.

Prognosis and Prediction

The prognosis for patients with this tumor is excellent, with only a single reported case with lymph node metastasis and no local recurrences in 30 cases with follow-up. All patients with this disease have been reported to be alive and disease-free at the time of last follow-up.

Clinical Features

Diagnostic Molecular Pathology

Not clinically relevant

Essential and Desirable Diagnostic Criteria

Essential: superficial location; large eosinophilic cells with granular to glassy cytoplasm; marked nuclear pleomorphism but a very low mitotic count; diffuse CD34 expression and frequent keratin immunoreactivity.

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