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SARCOMAS AFFECTING THE SKIN

Angiosarcoma

Angiosarcomas occur mainly in elderly men, predominantly on the head and neck (Figs 33.35). They may be relatively subtle clinically, representing bruises or thin purplish patches and plaques initially. Some cause more rapidly enlarging nodules, which may resemble Merkel cell carcinoma. Angiosarcoma arising in limbs (Figs 33.36), including development
within chronic lymphedema (angiosarcoma of Stewart and Treves ), is a particularly aggressive variant with a high risk of metastatic spread.
    Histologically, and sometimes clinically, the main differential diagnosis is Kaposi sarcoma. Treatment is with surgery and radiotherapy, but recurrences and metastases are common.

Kaposi sarcoma

Kaposi sarcoma (KS) has become a relatively common tumor in many parts of the world due to the association with AIDS. It is related to human herpesvirus 8. In AIDS-related KS, the lesions are usually multiple, purplish patches and plaques, which may occur on any part of the body; the palate is a particularly common site (Ch.12). Although this manifestation of AIDS is most frequent in homosexually acquired cases, KS also occurs as more indolent non-HIV-associated forms which mainly affect the lower leg (Figs 33.37), and which may be quite subtle and slowly progressive (e.g. after cytotoxic chemotherapy). There is also an endemic African form.
    Differential diagnosis is from other angiomatous lesions (including a benign proliferation related to venous stasis disease, known as pseudo-KS or acroangiodermatitis), from other sarcomas, and sometimes from vasculitis of the lower leg. Verrucous and lymphedematous variants may cause diagnostic problems.
    Treatment of AIDS, if this is relevant, is essential (see Ch. 12). Treatment options for the lesions include radiotherapy, cryotherapy, and intralesional or systemic interferon or other cytotoxic or chemotherapeutic agents.

Other sarcomas

Soft tissue sarcomas are an important group of lesions, most of which primarily affect deeper tissue but may affect the skin. The types most likely to be seen by dermatologists are discussed here. As a general guideline, it is important to consider this group of disorders in the differential diagnosis of large, deep, poorly defined nodules: they are often 5cm or larger at presentation, but may be deceptive in their extent. Wide excision is required; the local recurrence rate is significant if non-curative shelling out' is performed, and the pathologic features are often subtle and difficult.

Dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is usually a slowly growing, indurated nodule, which usually occurs on fleshy areas such as the thigh, buttock, or back, and which is covered with rather thinned, stretched skin (Figs 33.38). A subcutaneous extension may be palpable around it, and treatment requires wide excision laterally and in depth due to the high frequency of local recurrence. Histologically, these lesions can be difficult to distinguish from dermatofibromas, but immunohistochemistry is often helpful; DFSP is CD34-positive and negative for FXIIIa, by contrast with dermatofibromas, which are the opposite. Rare congenital cases are described.

Figure 33.38  Dermatofibrosarcoma protuberans, showing a group of small nodules that arose from a firm base. (Courtesy of Michael O. Murphy, M.D.) .

Malignant fibrous histiocytoma

Malignant fibrous histiocytoma may be clinically similar to DFSP but is usually more inflammatory and faster-growing. It affects mainly older individuals, and has a high frequency of both local recurrence and metastasis after excision. Other sarcomas such as the malignant peripheral nerve tumor, a rare and aggressive sarcoma, may be clinically and pathologically similar (Fig 33.39). Wide excision is the initial treatment for most sarcomas, but diagnosis and management may be difficult.

Atypical fibroxanthoma

Atypical fibroxanthoma resembles squamous cell carcinoma in its morphology, site (sun-exposed skin of scalp, ear, and dorsum of hand), and age group affected (mostly over 60 years) (Figs 33.40 and Figs 33.41). Ears seem to be relatively commonly affected. By contrast to the other sarcomas listed, local excision is usually curative.

Figure 33.39  Malignant fibrous histiocytoma, a type of cutaneous sarcoma. This growth pattern, with a central nodule but indurated lateral extension, is a frequent feature of skin sarcomas. Wide excision is required.

Figure 33.40 (a,b) Atypical fibroxanthomas. In these two cases, an identical site on the ear has been affected. Treatment is by excision of a disk of skin with the underlying cartilage, and the wound can be grafted or allowed to heal by second intention with excellent cosmetic result. (Panel a courtesy of Michael O. Murphy, M.D.)

Figure 33.41  A more aggressive lesion of atypical fibroxanthoma with ulcerated surface, which is clinically indistinguishable from a squamous cell carcinoma.

Leiomyosarcoma

These are rare sarcomas but may cause differential diagnosis problems clinically, as they are often relatively small and may be of dermal origin, with tethering that mimics dermatofibroma or a ruptured cyst. Histologically, they are spindle cell tumors with positive staining for smooth muscle actin. If multiple, then they should be assumed to be metastases from an internal soft tissue site. Retroperitoneal primary sites are often occult.

PRACTICE POINTS

•	If Kaposi sarcoma (KS) is considered, always examine the mouth: there may be oral hairy leukoplakia, candidiasis, or the purple plaques of mucosal KS.
•	Soft tissue sarcomas are generally more extensive than they appear to be clinically: beware the pitfall of the apparently simple shelling out' operation.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.