Lesions Reported as Plaque-Like CD34-Positive Dermal Fibroma Reveal Two Reproducible Clinicopathologic Patterns: Two...

Plaque-like CD34-positive dermal fibroma (PDF), which historically overlaps with medallion-like dermal dendrocyte hamartoma (MDDH), is a rare benign CD34-positive spindle-cell lesion with highly variable clinicopathologic descriptions. We analyzed two adult-onset cases and reviewed the published literature to determine whether reported PDF/MDDH lesions cluster into reproducible clinicopathologic patterns. Our literature review comprises 25 cases. Comparative analyses revealed marked differences in age at onset, lesion size, anatomic distribution, depth of involvement, papillary dermis sparing, subcutaneous extension, and epidermal response. One pattern was characterized by early-onset, larger plaque-like lesions on the trunk or neck, with deep dermal to subcutaneous spindle-cell proliferation and frequent epidermal atrophy (early-onset deep pattern). The second pattern was characterized by adult-onset, small papules or papuloplaques, predominantly on the extremities, featuring upper reticular dermal spindle-cell proliferation, papillary dermis sparing, elongated rete ridges, and a perpendicular-to-horizontal spindle-cell arrangement (adult-onset superficial pattern). All lesions showed diffuse CD34 positivity. Lesions currently reported under the PDF/MDDH umbrella appear to encompass two reproducible clinicopathologic patterns. Recognizing these patterns may improve diagnostic accuracy and facilitate the distinction of these lesions from dermatofibrosarcoma protuberans and other superficial CD34-positive spindle-cell proliferations.