Myxoid variant of plexiform fibrohistiocytic tumor: case report.

Background: Plexiform fibrohistiocytic tumor (PFH) is a rarely metastasizing slowly growing neoplasm usually affecting children and young adults. The tumor usually has a dermal-subcutaneous location, is poorly circumscribed, and is comprised of a plexiform or multinodular proliferation of a variable admixture of fibroblasts and histiocytoid cells with a distinctive biphasic morphology. Myxoid change in PFH is extremely rare with only five cases of myxoid variant of PFH reported to date in the English literature.

Case Description: In this case report, the author describes a rare case in a 39-year-old man who had presented with a newly developed right forearm mass. Given the tumor's unusual morphology an extensive immunohistochemical and molecular workup was performed to rule out common superficial myxoid neoplasms and potential mimickers. The overall ancillary findings along with the histomorphologic features and immunoprofile of the entirely excised mass were eventually compatible with myxoid PFH.

Conclusions: Myxoid PFH is a rare or underrecognized entity that can present as a diagnostic pitfall and can lead to an erroneous diagnosis especially if the pathologist is unaware of such entity. In this case report the author sheds light on this unique tumor, myxoid PFH, discusses the pitfalls inherent to its differential diagnosis, and reviews the literature on such a rare phenomenon.