Superficial CD34-Positive Fibroblastic Tumor

Abstract

Superficial CD34-positive fibroblastic tumor (SCD34FT) is a rare soft tissue neoplasm that shows overlapping features with PRDM10-rearranged soft tissue tumor (PRDM10-STT). This study characterizes the clinicopathologic, immunohistochemical, and molecular features of SCD34FT in a series of 59 cases. Fluorescence in situ hybridization to assess for PRDM10 rearrangement was performed in 12 tumors. Immunohistochemistry for CADM3 and WT1 was performed; CADM3 was also assessed in histologic mimics. Our cohort of 33 male and 26 female had a median age of 42 (range: 14 to 85) years. Tumors were most commonly located in the lower limb (73%), upper limb (8%), back (7%), and supraclavicular region (3%). The median tumor size was 3.0 cm (range: 1.0 to 9.0 cm). Clinical follow-up in 32 patients (median duration: 26 mo) revealed 2 local recurrences (6%). One patient developed regional lymph node metastases which were completely excised. Microscopically, SCD34FT comprised spindled and pleomorphic cells with glassy cytoplasm and occasional granular cell change. Fluorescence in situ hybridization confirmed PRDM10 rearrangement in 3/8 cases (38%). SCD34FT frequently expressed CADM3 (95%) and WT1 (75%). CADM3 was less diffusely positive in pleomorphic hyalinizing angiectatic tumor (40%), pleomorphic liposarcoma (20%), and undifferentiated pleomorphic sarcoma (10%). We corroborate that SCD34FT is indolent but may rarely metastasize to lymph nodes without adverse outcomes. CADM3 and WT1 may be useful in the distinction from histologic mimics. Since cases of SCD34FT with and without demonstrable PRDM10 rearrangement were clinicopathologically indistinguishable, our study further supports that SCD34FT and PRDM10-STT likely constitute a single entity.

Superficial CD34 fibroblastic tumors and PRDM10‐rearranged soft tissue neoplasm: An evolving diagnosis

“…Mitotic activity is generally low; however, atypical mitotic figures can sometimes be seen 7 . Recent studies have identified positive CADM3 immunohistochemical staining in up to 95% of both tumors regardless of PRDM10 rearrangement 3,6,7 . Anderson et al also recently described WT1 positivity in 75% of SCD34FTs and in all tumors with the PRDM10 rearrangement 7 .…”

“…Both tumors exhibit diffuse CD34 positivity, and a subset may also be positive for pan‐keratin and desmin 3 . Mitotic activity is generally low; however, atypical mitotic figures can sometimes be seen 7 . Recent studies have identified positive CADM3 immunohistochemical staining in up to 95% of both tumors regardless of PRDM10 rearrangement 3,6,7 .…”

“…Clinically, both tumors are usually superficial and predominantly occur on the lower extremities. Histopathologically, both tumors exhibit spindled and pleomorphic cells, lack necrosis, and commonly contain inflammatory infiltrates composed of lymphocytes, plasma cells, and histiocytes 3,6–8 . Other features may include ectatic hyalinized vessels and myxoid stroma 3,7 .…”

“…In addition, both tumors have similar biologic behavior, with a favorable prognosis 1,3 . These similarities brought the relationship between SCD34FT and PRT into question, regarding whether these are two separate entities or if they represent a single diagnosis 3,6,7 …”

“…Histopathologic features include poorly circumscribed spindle cells, ectatic vessels, low mitotic counts, and diffuse CD34+ staining 3,8 . While some SCD34FT can occasionally demonstrate large ectatic vessels, some distinguishing features seen in PHATs include a myxoid stroma and hemosiderin‐laden spindle cells at the periphery of the tumor 6,7 . In addition, about 60% of PHATs harbor OGA and TGFBR3 rearrangements 3,7 .…”