Track

Clinical Studies

Abstract

Cellular digital fibroma (CDF) is a small CD34-positive cutaneous spindle cell tumor of the digits. Some authors have debated the existence of CDF, arguing it is the same as superficial acral fibromyxoma (SAF). Loss of Retinoblastoma 1 (Rb1) by IHC and FISH was first reported in SAF in 2016. To our knowledge, no study has investigated Rb1 expression in CDF. We describe 10 CDFs, in 4 men and 6 women, ages 33-75 years (median 45). The mean size was 7.5 mm (range 3-12 mm). Sites included fingers (6), toes (2), palm (1), and “foot” (1). No recurrence was reported in the medical record for any case (follow up 29-201 months; median 128). Histology revealed a superficial dermal cellular proliferation of bland spindled fibroblasts in a collagenous stroma with fascicular or whorled/storiform arrangement. Surprisingly, colloidal iron highlighted abundant stromal mucin (9/10), which was not obvious on H&E. IHC showed CD34 expression (10/10); EMA and S100 were negative in all cases tested (9 and 7, respectively). Loss of Rb1 expression was observed in 80% (8/10); the remaining 2 cases had equivocal patchy Rb1 staining (these are pending RB1 FISH). Our results suggest that CDF is another entity in the expanding list of mesenchymal tumors with CD34 expression and Rb1 loss, a list that includes SAF. Although CDF may exist on a spectrum with SAF, we propose that CDF remains a useful nomenclature for small superficial lesions given the apparent low risk for local recurrence even without complete excision.