The Value of Immunohistochemistry in Atypical Cutaneous Fibrous Histiocytoma

Abstract

Atypical cutaneous fibrous histiocytoma is a rare variant of dermatofibroma/fibrous histiocytoma characterized by striking atypia, thus resembling atypical fibroxanthoma. We studied 9 examples of ACFH histopathologically and immunohistochemically to investigate the nature of these atypical cells. Histology revealed ill-defined skin nodules, which were polypoid in 6 cases. A minority of mononuclear and giant cells (< 5%) revealed striking pleomorphism and showed large nuclei with prominent nucleoli. Immunohistologically, the atypical cells expressed vimentin, but were negative for S-100 protein, the keratin marker MNF116, alpha smooth muscle actin, CD34, factor XIIIa, and monocyte/macrophage markers Ki-M1p, KP1 (CD68), and MAC387. Positivity for MiB1 was very modest (< 1%) and limited to small- and medium-sized, inconspicuous cells. Multinucleate giant cells proved to be heterogenous, on one hand cells with differentiation toward macrophages with positivity for Ki-M1p and KP1, on the other toward fibroblasts positive for vimentin only. These immuno-histochemical results for differentiation markers in atypical cutaneous fibrous histiocytoma are similar to our previous findings and data in atypical fibroxanthoma; MiB1 helps to separate these entities from each other as the latter shows a very high proportion of proliferative atypical cells corresponding to the numerous mitoses seen in routine sections.

Trichilemmal Cyst With Carcinoma In Situ Within an Atypical Fibroxanthoma

“…10) and were distinctly decorated with cytokeratins (Figs. 8,9) in contrast to the atypical cells within the AFX, which were negative for cytokeratin but strongly positive for CD10 (Fig. 5).…”

“…Similarly, tumors reported in the past as AFX appearing in non-sun-exposed skin of young individuals probably represent examples of atypical fibrous histiocytoma. 8 Immunocytochemical markers can help exclude these entities before the diagnosis of AFX is established. 9 The nonspecific lysosome marker CD68 has been shown to be variably positive in mononuclear (histiocyte-like and xanthomatous cells) and multinucleated cells (Fig.…”

“…8,9). Therefore, morphological features along with the immunoprofile of the tumor allowed the diagnosis of a trichilemmal cyst with carcinoma in situ within the wall in an AFX.…”

A Case of Atypical Fibrous Histiocytoma with Positivity for CD163 and CD44

“…Kaddu et al (2) reported the presence of 1-15 pathologic mitoses per 10 high power field (HPF) (mean 3.4 per 10 HPF) (20/59 cases, 33.9%) and/ or geographic-like necrosis (7/59 cases, 11.9%) (2). Many reports have indicated positivity for factor Xllla (4-6), but negativity has also been reported in sotne cases (2,7,8). Garrido-Ruiz et al (6) and Wilk et al (8) reported that AFH was CD34-negative.…”

Study of Epithelial to Mesenchymal Transition in Atypical Fibroxanthoma and Undifferentiated Pleomorphic Sarcoma to Discern an Epithelial Origin

“…However, the tumoral Ki-67-positive proliferative cells lack Ki-M1p, a macrophagic marker, thus suggesting that macrophages are an accompanying background population. 7 The positivity of the cells of AFX to vimentin might suggest a mesenchymal origin. Accordingly, AFX has been shown to display myofibroblastic differentiation with the aid of electron microscopy.…”