CORRECT DIAGNOSIS:
Collagenous fibroma (desmoplastic fibroblastoma)
DISCUSSION:
Desmoplastic fibroblastoma (DF), also known as collagenous fibroma is a distinct yet uncommon benign fibrous soft tissue tumor that typically occurs in the subcutaneous tissue or skeletal muscle in adults. Since first described in 1995 by Evans, fewer than 100 cases have been reported in the English literature. Clinically, the lesion usually presents as a well-circumscribed, firm, painless, slow-growing mass of several months duration and can range greatly in size; up to 20 cm. It most commonly appears in males with a peak incidence in the fifth and sixth decade of life. Lesions can appear in a variety of locations with the most common sites being the forearm, shoulder, upper leg, and feet.
Histologically, the tumor appears well defined with normal overlying epithelium. The tumor is composed of sparsely distributed stellate or spindled fibroblastic cells with bland cytologic features separated by abundant intercellular collagen fibers. Blood vessels, necrosis, and mitotic figures are typically absent. Immunohistochemical stains are useful in diagnosis with the tumor cells showing a fibroblastic-myofibroblastic compatible profile. The cells are intensely positive for vimentin and show variable expression for SMA. Staining for desmin, S100, CD34, and EMA is typically negative.
Interestingly, a few recent studies have found desmoplastic fibroblastomas to be associated with clonal chromosome aberrations, specifically rearrangement of chromosome 11q12. This finding further supports the original designation for this entity as a “neoplasm” versus the possibility of a reactive process.
TREATMENT:
Adequate treatment of desmoplastic fibroblastomas is achieved with simple conservative excision, with no reported recurrences in the literature. Dermatologists and pathologists should beware of the existence of this tumor so that proper diagnosis and treatment can be employed, thereby avoiding unnecessarily aggressive surgery.
REFERENCES:
Evan, H. L. (1995). Desmoplastic fibroblastoma. American Journal of Surgical Pathology, 19(10), 1077-1081. https://doi.org/10.1097/00000478-199510000-00002
Miettinen, M., & Fetsch, J. F. (1998). Collagenous fibroma (desmoplastic fibroblastoma): A clinicopathologic study of 63 cases of a distinctive soft tissue lesion with stellate-shaped fibroblasts. Human Pathology, 29(7), 676-682. https://doi.org/10.1016/S0046-8177(98)90247-1
Hasegawa, T., Shimoda, T., Hirohashi, S., Hizawa, K., & Sano, T. (1998). Collagenous fibroma (desmoplastic fibroblastoma): Report of four cases and review of the literature. Archives of Pathology & Laboratory Medicine, 122(5), 455-460. PMID: 9581586
