GRANULAR-CELL DERMATOFIBROMA

Aims: To describe a series of five granular cell dermatofibromas as an unusual and rare manifestation of fibrohistiocytic tissue response. M ethods and results: Five granular cell dermatofibromas were collected out of 136 tumours filed as granular cell tumours. Clinically, all les ions occurred on the shoulder or back of middle-aged adults (two women , three men), mostly with the clinical diagnosis of a fibrohistiocytic lesion. Histology revealed well-circumscribed, dermal to subcutaneous lesions dominated by periodic acid-Schiff (PAS) positive, granular ce lls. Acanthosis above, as well as storiform arrangement of spindle cel ls, sclerotic collagen and some interspersed lymphohistiocytic infiltr ate at the periphery of the lesion, indicated the fibrohistiocytic ori gin. Lesions showed prominent reactivity with NK1C3 (CD57), as well as for macrophage markers KiM1p and KP1 (CD68), In contrast to classic S chwannian/neurogenic granular cell tumours, granular cell dermatofibro mas were S100 protein negative, but showed variable reactivity for fac tor XIIIa (10-50%) in 4/5, for smooth muscle specific actin (10-50%) i n 2/5 and with E9 (10-30%) in 3/5 lesions, Electron microscopy in one case revealed large pools of phago-lysosomes and variably sized glycog en granules in granular cells. Conclusion: Our series delineates granu lar cell dermatofibroma as a distinct clinicopathological variant of f ibrohistiocytic tissue response which needs to be distinguished from o ther tumours with granular cell features.