Fibroxanthoma atypical C49; D48.1

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 01.12.2022

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AFX; atypical fibroxanthoma; Atypical fibroxanthoma; Cutaneous malignant histiocytoma; Fibrosarcoma paradoxes; paradoxical fibrosarcoma; Pleomorphic malignant fibrous histiocytoma; pseudocarcinoma; Pseudocarcinoma; Pseudosarcomatous reticulohistiocytoma; Pseudosarcomatous xanthofibroma; Xanthofibroma pseudosarcomatous

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Hellwig, 1961 (published 1963)

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Rare, solitary, intermediate malignant fibrohistiocytic tumour of the skin, growing rapidly within a few months, with a relatively benign clinical course, occurring almost exclusively in light-damaged skin of elderly people. Probably it is not an independent clinical picture but a reaction pattern of different, largely undifferentiated neoplasias, but also degenerative processes. Thus, squamous epithelial carcinomas, melanomas, basal cell carcinomas, pseudosarcomatous xanthogranuloma variants, etc. are concealed behind this fine-tissue reaction pattern. Some authors regard the atypical fibroxanthoma as a cutaneous variant of the malignant fibrous histiocytoma (Cooper JZ et al. 2005).

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The incidence is 2.5/100,000; m>w;

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UV as well as a previous irradiation therapy with X-rays seem to play a decisive pathogenetic role; furthermore, a persistent immunodeficiency (increase of AFX in organ transplant patients) as well as genetic defects such as those e.g. in xeroderma pigmentosum.

Mutations in the tumor suppressor gene p53 have been increasingly found and are thought to have pathogenetic relevance. Furthermore, telomerase reverse transcriptase (TERT) promoter mutations have been detected. These mutaions lead to cell immortalization through activation of telomerases and (Grievank KG et al. 2014).

Histogenesis is still unclear: the likely origin is from poorly differentiated mesenchymal cells of origin, possibly histiocytes or fibroblasts. Proliferations of dedifferentiated keratinocytes are also suspected (in individual cases a focal keratin expression was detected), a myoblastoid proliferation, a proliferation of Langerhans cells and others.

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The initial manifestation is particularly frequent during two age peaks, in the 4th and 7th decade respectively, with the latter being significantly larger (in a larger study - Mahalingam S. et al.- the average age was 75.9 years). The first peak refers mainly to non-light-damaged areas (extremities, trunk).

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Especially ears, nose, cheeks, neck, capillitium. In younger people also extremities or trunk.

Clinical features
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In actinically pre-damaged skin, there is a solitary, up to 3.0 cm large, coarse, indolent, skin-colored, red or brown-red, firm knot with a smooth atrophic surface, which often cannot be displaced on its base (infiltration of the subcutaneous fatty tissue). Often ulcerated and thus encrusted or diffusely bleeding surface.

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Usually well-demarcated nodule confined to the dermis and not extending into the subcutaneous adipose tissue (different from pleomorphic dermal sarcoma) consisting of atypical, spindle-shaped or pleomorphic cells with vesicular or bizarre, hyperchromatic nuclei. Bizarrely configured multinucleated giant cells and atypical mitoses are frequently encountered.

A definitive immunohistochemical marker for unequivocal diagnosis of atypical fibroxanthoma is lacking to date. The cells are CD34, S100, desmin, HMB-45 (human melanoma black 45) negative
(Koch M et al. 2015) (DD: dermatofibrosarcoma protuberans) as well as constant vimentin positive. Furthermore, inconstant reactivity for alpha smooth muscle actin and for CD68 is found. Occasionally, focal keratin expression is observed (so-called keratin-positive AFX). Furthermore, numerous vascular incisions are found. Frequent focal hemorrhages. Cellular variants with pigmentation and granular or clear cell degeneration are possible.

Myxoid sections are not uncommon and may also dominate the histologic picture. Molecular pathology: detection of p53 mutations and TERT promoter mutations provide evidence of UV induction of the tumor.

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The clinical findings are not very specific. The histological pattern and especially immunohistochemistry is diagnostically important for AFX.

Differential diagnosis
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  • Clinical:
  • Histological:
    • Carcinoma, spinocellular, desmoplastic: Fine strands or smaller tumor cell nests with atypical, very polymorphic keratinocytes surrounded by a broad desmoplastic stroma. The tumour tends to infiltrate along autochthonous structures such as nerves or vessels. Tumor cells are cytokeratin - and occasionally vimentin - positive.
    • Melanoma, malignant, desmoplastic: Fascicular or nodular cell trains of atypical, hyperchromatic, spindle cells located between fibrotically dense collagenous fibres. Occasional mitoses. Desmoplastic melanomas show neurotrophy and follow the course of the dermal nerves (desmoplastic-neutral melanoma). Immunohistology: S-100-, (HMB-45-, Melan A- are not always positive) and vimentin positive (!); S-100 is the most reliable marker.
    • Undifferentiated pleomorphic sarcoma (UPS): The AFX is probably the superficial variant of the UPS.
    • Malignant fibrous histiocytoma (MFH): This "controversial" tumor species should not be a true differential diagnosis, because UPS and MFH are probably identical tumors (see note).
    • Leiomyosarcoma: reactivity for smooth muscle actin and (inconstant) desmin. h- caldesmon +; cytokeratin +/-.

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Tendency to local recurrence (7-9%). These usually occur within a period of 1-2 years. Very rarely metastasis (0.5-4%) mostly in the regional lymph nodes followed by liver, lung and subcutis.

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Excision with a safety margin of at least 0.5 cm. Microscopically controlled surgery is now considered "state of the art".

Radiation therapy
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Radiation therapy can be used as an alternative in cases of unfavourable surgical site. Response only at higher doses (about 60-65 Gy).

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Favourable prognosis with complete excision on all sides. A metastasis is rare (note: older statistics show a metastasis rate between 0,5%-10%).

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Follow-up should be every six months for the first two years. In the third to the fifth year, annually. Follow-up includes clinical examinations of the patient.

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Many authors postulate an identity of malignant fibrous histiocytoma (MFH) and undifferentiated pleomorphic sarcoma (UPS). Histologically it is not possible to distinguish between MFH and UPS. The atypical fibroxanthoma is again considered to be a (superficial) dermal variant of this tumor species.

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  1. Cooper JZ et al (2005) Metastasizing atypical fibroxanthoma (cutaneous malignant histiocytoma): report of five cases. Dermatol Surgery 31: 221-255
  2. Eckert F et al (1990) The atypical fibroxanthoma. dermatologist 41: 39-42
  3. Fretzin DF, Hellwig EB (1973) Atypical fibroxanthoma of the skin. Cancer 31: 1541
  4. Griewank KG et al (2014) TERT promoter mutations are frequent in atypical fibroxanthomas and pleomorphic dermal sarcomas. Mod Catholic 27:502-508.
  5. Helwig EB (1963) Atypical fibroxanthoma. Tex J Med 59: 664-667
  6. Hilgers M et al (2014) Atypical fibroxanthoma of the capillitium. Dermatologist 65: 1008-1010
  7. Hill H (2006) Fibrohistiocytic skin tumors. J Dtsch Dermatol Ges 4: 544-555
  8. Koch M et al (2015) Atypical Fibroxanthoma - Histological Diagnosis, Immunohistochemical Markers and Concepts of Therapy. Anticancer Res 35:5717-5735.

  9. Iorizzo LJ et al (2011) Atypical fibroxanthoma: A review of literature. Dermatol Surgery 37: 146-157

  10. Mahalingam S et al (2015) Atypical Fibroxanthoma: A case series and review of literature. Auris Nasus Larynx. 42:469-471
  11. Rizzardi C et al (2003) Atypical fibroxanthoma and malignant fibrous histiocytoma of the skin. Anticancer Res 23: 1847-1851
  12. Stepanova A et al (2005) A rare low-grade malignant scalp tumor Atypical fibroxanthoma. dermatologist 56: 679-683


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Last updated on: 01.12.2022