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Angiomatoid fibrous histiocytoma (AFH) is a rare tumor of intermediate malignancy. Treatment options for unresectable and/or metastatic tumors are very limited. Immunotherapy with PD-1/PD-L1 inhibitors may be worth exploring. The aim of this study was to evaluate the expression of PD-L1 in AFHs. PD-L1 expression was assessed on 36 AFHs from 36 pediatric patients by immunohistochemical staining of PD-L1 (clone 22C3). Positivity was defined as membranous expression in ≥ 1% of either tumor or immune cells. The correlations between PD-L1 expression and clinicopathologic features were assessed. Two patients had lymph node metastasis. All patients underwent surgical resection; three of them also had systemic chemotherapy. Three patients had recurrence after initial resection; all patients were alive with a median follow-up of 2.5 years. Overall, twenty-two (61%) tumors were positively stained for PD-L1 and positivity was seen on both tumor and immune cells in eighteen of the 22 tumors. A positive correlation was found between tumor cell PD-L1 expression and CD8+ T-cell infiltration. There were no statistically significant differences between the status of PD-L1 expression and the clinicopathological features assessed. PD-L1 expression was identified in 61% of AFHs with a predominantly adaptive pattern. Our findings provide a rationale for future studies evaluating the potential of checkpoint immunotherapy for patients with unresectable and/or metastatic tumor.

Fibrous histiocytoma (FH) or dermatofibroma is a common cutaneous lesion mostly seen in adults and rare in the first two years of life. Two hundred sixty-seven patients younger than 18 years with a diagnosis of FH or dermatomyofibroma, a lesion with morphologic overlap with FH, were identified from the files of a single institution, with only 13 (4.8%) occurring in patients younger than 5 years. Ten patients had either underlying neurologic, autoimmune, or metabolic disorders or a family history of autoimmune conditions. Histologic review of hematoxylin and eosin staining and immunostaining on 75 FHs and dermatomyofibroma in 70 patients showed the following results: 33 classic FHs, 8 classic FHs characterized by a peculiar retiform morphology with thin fascicles of elongated cells forming a network reminiscent of the eruptive variant of FH, 19 deep/cellular variants, 5 aneurysmal variants, 3 lipidized variants (including two lesions in a patient affected by mucopolysaccharidosis IV), 3 dermatomyofibromas, and 4 isolated cases of hemosiderotic, granular cell atypical, and epithelioid FH. Immunostaining for factor XIIIa highlighted a dense network of dendritic cells in FH, which was significantly reduced in the FH with retiform morphology. Smooth muscle actin staining was positive in a high percentage of FHs (85.3%). The current series demonstrates that FH in children may show unique clinical and morphologic features. The retiform pattern with decreased dendritic cells found in congenital lesions and in two older patients with lesions in two locations might have a different pathogenesis, probably related to an altered immune response in very young patients., (Copyright © 2020 Elsevier Inc. All rights reserved.)