[Superficial CD34-positive fibroblastic tumor: a clinicopathological analysis of 25 cases]

Objective: To investigate the clinicopathological features and immunophenotype of superficial CD34-positive fibroblastic tumor (SCDFT) with an emphasis on differential diagnosis. Methods: The clinicopathological data and immunohistochemical profiles of 25 cases of SCPFT diagnosed from March 2015 to June 2020 in Department of Pathology, Fudan University Shanghai Cancer Center, China were analyzed. The literature was reviewed. Results: There were 14 males and 11 females, with the age at presentation ranging from 16 to 60 years (mean 38 years; median 40 years). Tumor occurred in the thigh (n=9), buttock (n=4), upper arm (n=3), shoulder (n=2), waist (n=2), lower leg (n=2), chest wall (n=1), abdominal wall (n=1) and vulva (n=1). Most of the patients presented with a slowly growing cutaneous nodule, with a mean diameter of 2.6 cm (range 1-5 cm). The duration of symptoms ranged from 1 week to 30 years. Microscopically, most of the tumors were located in the deep dermis to superficial subcutis. They were well circumscribed but frequently showed focal infiltration into adjacent adipose tissue. Tumor cells were composed of fascicles and sheets of spindled to polygonal cells with abundant eosinophilic cytoplasm possessing frequent granular or glassy appearance. Lipidized cells were also present. The striking feature was the presence of hyperchromatic pleomorphic cells, containing conspicuous nucleoli and intranuclear pseudoinclusion. Mitotic activity was very low. Besides, there were inflammatory infiltrates in the stroma. All tumors showed strong and diffuse immunohistochemical staining of CD34, with frequent focal expression of CKpan and occasional immunoreactivity of desmin. Follow-up data, which were available in 18 patients (range 7 to 69 months), showed a local recurrence in one patient and disease-free in all others. Conclusions: SCPFT is a newly-recognized low-grade fibroblastic tumor. Due to the marked nuclear pleomorphism, it is not uncommon to misdiagnose SCPFT as other pleomorphic mesenchymal tumors. Familiarity with its clinicopathological characteristics is helpful in avoiding overdiagnosis and overtreatment.