Fibroblastic connective tissue nevus (FCTN) represents a rare and distinct benign cutaneous mesenchymal lesion of fibroblastic/myofibroblastic lineage, which broadens the spectrum of lesions presently recognized as connective tissue nevus. A series of 25 cases of FCTN has been analyzed to further characterize the clinicopathologic spectrum and immunohistochemical features of this entity. Sixteen patients were female (64%) and 9 were male (36%), with age at presentation ranging from 1.5 months to 58 years (median, 10 y). Most patients presented with a solitary, slowly growing, painless plaque-like or nodular skin lesion. Eleven cases (44%) arose on the trunk, 9 (36%) on the head and neck, and 5 (20%) on the limbs. The lesion was present for a median duration of 11.5 months (mean, 13.2 mo). Grossly, the lesions were tan-brown to tan-white, smooth, and firm. Their size ranged from 0.3 to 2.0 cm in greatest dimension (mean size, 0.67 cm; median, 0.6 cm). All tumors showed poor circumscription and were situated primarily in the reticular deep dermis, extending into the superficial subcutis in 13 cases (52%). The lesion was associated with papillomatous epidermis in 17 cases (70%) and the presence of adipose tissue in the reticular dermis in 14 cases (60.9%). All tumors were composed of a proliferation of bland intradermal fibroblastic/myofibroblastic cells with indistinct palely eosinophilic cytoplasm and tapering nuclei, with no significant cytologic atypia or pleomorphism, arranged in short-intersecting fascicles and entrapping appendages. No mitoses were identified. Immunostains showed positivity for CD34 in 20 of 23 cases (87%) and weak focal positivity for smooth muscle actin in 9 of 19 cases (47%). No case stained positively for desmin or S100 protein. Clinical follow-up was obtained for 14 patients (median duration, 4 y). No tumor recurred locally, even when surgical excision was incomplete. No lesion metastasized. FCTN occurs most commonly as a plaque on the trunk and head/neck of children, involves deep dermis and superficial subcutis, and stains mainly for CD34. FCTN most likely represents a localized developmental dermal anomaly; it is entirely benign and should not be confused with dermatofibrosarcoma protuberans or other neoplasms such as dermatomyofibroma.
*Department of Pathology, Brigham and Women’s Hospital
†Department of Pathology, Harvard Medical School, Boston, MA
Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article.
Presented in part in March 2012 at the 101st annual USCAP meeting in Vancouver, BC, Canada.
Correspondence: Christopher D.M. Fletcher, MD, FRCPath, Department of Pathology, Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115 (e-mail: firstname.lastname@example.org).