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Background PReferentially expressed Antigen in Melanoma (PRAME) has been widely investigated in the skin, mainly in melanocytic tumors, and constitutes an aid in differentiating benign from malignant lesions. Very few others studies have been performed on non-melanocytic tumors. Materials We investigated the immunohistochemical expression of PRAME on a series of 11 neurothekeomas, together with three cases of nerve sheath myxoma and one case of plexiform fibrohistiocytic tumor, in order to evaluate the presence and usefulness of this marker in their differential diagnosis. Results PRAME was variably expressed in all cases of NTK, with moderate intensity in three cases, and faint in the remaining cases; on the contrary, cases of NSM and PFT were negative. Conclusions This study expands the entities of cutaneous non-melanocytic tumors expressing PRAME, and confirms that this marker is not restricted to malignant tumors. Expression of PRAME in NTK does not seem to be related to distinctive histopathologic features. This article is protected by copyright. All rights reserved.

Background: Atypical fibroxanthoma (AFX) is a locally destructive, dermal-based, fibrohistiocytic, mesenchymal tumor. Immunohistochemistry helps to differentiate AFX from squamous cell carcinoma and spindle cell melanoma. Immunomarkers against p75 yield positive stains in spindled cell melanomas and negative stains in AFX, suggesting that these may be useful in differentiating these two entities. However, a recent study concluded that p75 is not a specific marker of neuroectodermal tumors; furthermore, p75 staining in AFX has only been evaluated in a few cases. Methods: We stained 20 AFXs for p75 and various other markers. Results: Reactivity was noted for vimentin (20 of 20 cases), CD10 (17/20), CD68 (14/20), CD99 (13/20), D2-40 (10/20) and p75 (1/20). Conclusions: We confirmed that CD99 and CD10 are frequently expressed in AFX (65 and 85%, respectively) and that CD31 rarely stains positive (5%). The 50% positivity rate of D2-40, in contrast with published evidence for its absence in melanoma, suggests that D2-40 may be useful for distinguishing AFX from melanoma. Furthermore, because only one sample was positive for p75, we confirm that p75 is useful in differentiating AFX from spindle cell melanoma. We advocate adding p75 and D2-40 to assist in differentiating AFX from melanoma. Bull C, Mirzabeigi M, Laskin W, Dubina M, Traczyc T, Guitart J, Gerami P. Diagnostic utility of low-affinity nerve growth factor receptor (P 75) immunostaining in atypical fibroxanthoma.

Atypical fibroxanthoma (AFX) is an uncommon cutaneous neoplasm of pleomorphic myofibroblast-like cells. Diagnosis requires exclusion of other undifferentiated spindle and pleomorphic cell neoplasms by immunohistochemistry. We report two patients with p63-non-reactive spindle cell neoplasms which resembled AFX but demonstrated anomalous dot-like immunolabeling with antibodies to high molecular weight keratin and keratin 5. One case recurred locally, suggesting such lesions may behave aggressively. Whether these lesions represent keratin-positive dermal sarcomas or poorly differentiated carcinomas is debatable. Regardless of exact classification, our experience suggests such cases should be managed as high-risk non-melanoma skin cancers.

Atypical fibroxanthoma (AFX), a benign lesion, and pleomorphic malignant fibrous histiocytoma (MFH) are thought to represent points along the same neoplastic spectrum but with different prognoses and treatments. Diagnosis based on histology and clinical parameters alone is sometimes difficult, and a reliable cost-effective immunohistochemical marker to help distinguish these lesions would be beneficial. The diagnosis of AFX or MFH was based upon published clinical and microscopic criteria. Formalin-fixed, paraffin-embedded tissues of 17 cases of AFX and 26 cases of MFH were immunostained with monoclonal antibody to CD99. For all cases, CD99 expression was scored on a four-tiered scale: negative, weak (1+), moderate (2+), or strong (3+). Two pathologists blinded to tumor diagnoses and type of immunostain evaluated each case independently. The interobserver correlation coefficient was calculated. Seventeen patients with AFX (16 males and one female; mean age = 79) and 26 patients with MFH (16 males and 10 females; mean age = 60) were included. AFX lesions were from the head and the face, mean size = 1.5 cm, and MFH lesions were from the head, the neck, the trunk, and the upper/lower extremities, mean size = 5.2 cm. The 17 cases of AFX demonstrated moderate or strong (2 to 3+) immunoreactivity with CD99, compared to nine of 26 (35%) MFH cases (chi-square = 18.38; p < 0.001; interobserver correlation coefficient = 0.83). Of these, 16 of 17 (94%) AFX cases stained diffusely with CD99, while only four of 26 (15%) MFH cases stained diffusely. Control slides were adequate. Our study demonstrated that CD99 can help distinguish AFX from MFH, in addition to other immunohistochemistry as well as clinical and histologic criteria.

We report two cases of atypical fibroxanthoma (AFX) that both had the previously unreported feature of neural invasion (one perineural and the other intraneural). AFXs recur in approximately 10% of cases but only rarely metastasize. Features associated with recurrence are inadequate excision and invasion into fat. Features associated with metastasis include recurrence, vascular invasion, deep tissue invasion, and tumor necrosis. Both of these tumors invaded deeply into subcutaneous fat and reached the deep fascia. Some authors would regard such cases as malignant fibrous histiocytoma (MFH) because of such deep extension; however, the concept of AFX as a superficial variant of MFH is outmoded--AFX is a distinct clinicopathologic entity with established clinical, histological, and immunohistochemical features.

Background: Epithelioid fibrous histiocytoma (EFH) represents a morphologic variant of cutaneous fibrous histiocytoma (FH) but can lack many characteristic features. The presence of epithelioid cytomorphology may mimic other dermal neoplasms. Our anecdotal experience of epithelial membrane antigen (EMA) expression in some examples of EFH has caused diagnostic difficulty. Our aim was to examine the immunohistochemical profile and incidence of EMA expression in EFH. Methods: Forty-four cases of EFH were retrieved from consultation files. Clinicopathologic and immunohistochemical features were evaluated. Results: Membranous EMA positivity was found in tumor cells in 27/42 cases (64%). Focal positivity for factor XIIIa was found in 10/14 (71%) and D2-40 in 14/27 (52%). Scattered smooth muscle actin (SMA)-positive tumor cells were seen in 11/43 (25%). Focal positivity for claudin-1 was found in 3/42 (7%). CD163 staining highlighted stromal macrophages; however, in five cases it was difficult to exclude focal staining of tumor cells. Tumor cells were consistently negative for pan-keratin, AE1/AE3, S100, CD31, CD34, CD68, desmin, p63, GFAP and CD45/LCA. Conclusion: Frequent EMA expression in EFH represents an unexpected finding and constitutes a potential diagnostic pitfall. Although of uncertain significance, this finding, when combined with established morphologic differences, raises the possibility that EFH is unrelated to classic FH. Doyle LA, Fletcher CDM. EMA positivity in epithelioid fibrous histiocytoma: a potential diagnostic pitfall.

Myxofibrosarcoma is one of the most common soft tissue sarcomas occurring in older adults. It can arise de novo or can be radiation induced, and the term myxofibrosarcoma was originally devised to encompass a spectrum of myxoid tumors with characteristics similar to malignant fibrous histiocytoma (MFH). Confusion exists, however, regarding the distinction between microscopic grade and characteristics of myxofibrosarcoma and MFH. Correct classification is vital to prognosis, as the degree of myxoid change is inversely related to the incidence of metastasis. We present a case of a 76-year-old man with a history of high-grade MFH of the left lower extremity, status post excision and radiation therapy, who presented 2 years later with a regional metastatic recurrence of high-grade MFH to the left groin as well as new nodules adjacent to and within his prior excision and radiation site. These new nodules were determined to represent low-grade myxofibrosarcoma. These new low-grade lesions either represent a low-grade recurrence of high-grade sarcoma or a new, radiation-induced soft tissue sarcoma occurring at the same site. Radiotherapy, however, is an unlikely cause; specific postradiation sarcoma criteria have not been fulfilled. This article discusses both the nosology and histopathological spectrum of these important soft tissue sarcomas, their aggressive and recurrent nature and their association with radiation therapy. Bandino JP, Norton SA, Aldrich SL, Wisco OJ, Hodson DS, Murchland MR, Grande DJ. Low-grade myxofibrosarcoma presenting at the site of prior high-grade disease.