Track

Case Reports

Abstract

Superficial CD34+ fibroblastic tumor (SCD34FT) is a relatively recently described borderline mesenchymal neoplasm. Due to lack of specific clinical presentation, radiopathologic findings, and immunohistochemical (IHC) staining, diagnosing SCD34FT is challenging. Here, we present a case of a 55-year-old female with a singular, indolent round to oval painless nodule on the right shin. Histopathologic evaluation of the resected specimen showed a subcutaneous moderately cellular lesion composed of oval to spindled cells with mild pleomorphism arranged in sheets and fascicles in collagenous to hyalinized stroma, with limited extension into the adjacent adipose tissue. IHC staining demonstrated that the tumor cells were strongly and diffusely positive for CD34. Surprisingly, the tumor cells showed diffuse expression of SMA and more than focal (subset to diffuse) expression of AE1/AE3 and CAM5.2. DNA and RNA next-generation sequencing revealed t(X;11)(q13;q24) MED12::PRDM10 fusion. The constellation of  histomorphologic and molecular findings supports the diagnosis of SCD34FT. This case highlights a case of SCD34FT with a more extensive immunoreactivity to epithelial markers (AE1/AE3 and CAM5.2) and SMA compared to focal staining reported in the existing literature. We hope that adding this case to the existing literature will raise awareness among pathologists to recognize the more variable staining pattern of epithelial markers and SMA when considering the diagnosis of SCD34FT.