Abstract: 【Abstract】 Objective To investigate clinical, histopathological, molecular genetic characteristics, and immunophenotypes of superficial CD34-positive fibroblastic tumor （SCPFT）. Methods The pathological data were collected from 19 cases of SCPFT from January 2015 to July 2022 in the First Affiliated Hospital of Nanjing Medical University, and analyzed retrospectively. Results In total, 19 cases of SCPET were enrolled, including 8 males and 11 females. Their age at onset ranged from 16 to 67 years, and the disease duration ranged from 3 months to 3 years. Tumors occurred in the thigh （6 cases）, back （4 cases）, shoulder （3 cases）, abdominal wall （2 cases）, popliteal fossa （1 case）, lower leg （1 case）, foot （1 case） and forehead （1 case）. The tumor lengths were 0.8 - 4 （2.36 ± 0.76） cm, with relatively clear borders. Surgical excision was performed in all the 19 cases, and 1 case experienced recurrence. Histopathological examination showed that tumors were located in the dermis and subcutis, and infiltrated the peripheral fat tissues or the dermis; tumors were composed of abundant spindle cells and polygonal cells arranged in interlacing fascicles; cells with nuclear pleomorphism were observed in all cases, and were characterized by large, hyperchromatic and irregular nuclei, intranuclear pseudoinclusions, and prominent nucleoli; the mitotic figure was rare, and tumor necrosis was not found; inflammatory cell infiltration to different extents was observed in the tumor stroma, and lymphocyte sheaths were observed around the tumors in 2 cases. Immunohistochemical staining showed strong diffuse expression of CD34 in the tumor cells in all the 19 cases, the Ki-67 proliferation index was < 10% in 18 cases, and CKpan （2/12）, desmin （2/15）, and smooth muscle actin （1/19） were focally expressed. Fluorescence in situ hybridization for the detection of PRDM10 gene rearrangements was performed in 3 cases, and identified PRDM10 rearrangements in 2 cases, including 1 case of SCPFT accompanied by lymphocyte sheaths without EWSR1 rearrangements. Conclusion SCPFT is an intermediate fibroblastic tumor with no characteristic clinical manifestations, often accompanied by PRDM10 rearrangements, and its diagnosis depends on histopathological patterns.

Key words: Soft tissue neoplasms, Skin neoplasms, Pathology, Diagnosis, differential, Fibroblasts