br Introduction Malignant melanoma may simulate various type

Introduction Malignant melanoma may simulate various types of soft tissue tumor, such as dermatofibrosarcoma protuberans, malignant fibrous histiocytoma (MFH), myxofibrosarcoma (myxoid MFH), malignant hemangiopericytoma, and malignant schwannoma. Malignant melanoma mimicking atypical fibroxanthoma (AFX) appears to be very rare, only four reported cases being found in a Medline search.
Case report A 72-year-old Taiwanese woman presented with a 2-year history of two asymptomatic, enlarging nodules on her left cheek. Examination revealed two erythematous, dome-shaped nodules measuring 0.9 × 0.6 cm and 0.6 × 0.5 cm, respectively, within a large hypopigmented patch (Figure 1). Biopsy specimens of both lesions showed well-circumscribed cellular nodules in the reticular dermis separated from the overlying flattened epidermis by a zone of solar elastotic or fibrotic upper dermis (Figure 2A). The nodules consisted primarily of sheets of atypical epithelioid pyruvate dehydrogenase kinase arranged in vague nesting pattern (Figure 2B), as well as giant or gigantic cells with two or more large pleomorphic nuclei (Figure 2C). Both types of atypical cell had large hyperchromatic, and one or more vesicular, nuclei, mostly with a prominent nucleolus, and moderate-to-abundant eosinophilic cytoplasm. Some giant cells also had foamy cytoplasm in places (Figure 2C). However, close inspection revealed some atypical melanocytes in the epidermis with pagetoid spread in one small focus away from the dermal nodules (Figure 3). Fontana-Masson staining revealed an absence of melanin in the tumor nodules and reduced pigmentation in the overlying epidermis. The tumor cells showed a moderate-to-strong expression of S-100, Melan-A, and HMB-45 (Figure 4). The pleomorphic giant cells were focally CD68-positive but CD163-negative (not shown). Based on the pathological findings, AFX-like amelanotic malignant melanoma, with a Breslow thickness of 3.4 mm and a Clark level of IV, was diagnosed.
Discussion We have described here a rare case of AFX-like malignant melanoma manifesting as two amelanotic nodules on the cheek of an elderly Taiwanese woman. Interestingly, both nodules were located within a large hypopigmented patch, a finding suggestive of the halo phenomenon. Malignant melanoma may have a wide variety of clinicopathological presentations, but the AFX-like variant is very rare. Four cases of this variant have been reported, and their findings are summarized in Table 1. AFX is a tumor that was first described by Helwig in the 1960s and is believed to be of fibrohisiocytic origin. Most AFX tumors display a rapidly growing, ulcerated or bleeding nodule on the sun-damaged skin of an elderly person. Although AFX has the capacity for local recurrence or even metastasis, it is usually cured by complete excision. AFX-like melanoma, however, has a much worse prognosis. In the three cases of AFX-like melanoma described by Sangueza and Zelger (Table 1), all the lesions were found on the faces of elderly patients, and the diagnosis was delayed due to the unusual clinicopathological presentations. Two of three patients died due to rapid recurrence or metastasis. Previous reports have highlighted the difficulties in distinguishing malignant melanoma from AFX, and the use of immunohistochemistry is often necessary. Characteristic markers of melanomas such as S-100 protein, Melan-A/MART1, and HMB45 are not expressed in classic AFX. However, melanomas may rarely be S100-protein negative, and not uncommonly Melan-A/MART1-, HMB45-, and/or NKIC3-negative. In one AFX-like melanoma reported by Sangueza and Zelger, the diagnosis was delayed due to the negative results for S-100, Melan-A, and HMB45 in the first excisional specimen. CD68 expression is variable in AFX and MFH, so is not very useful for distinguishing these tumors from spindle cell melanomas. Smith-Zagone et al showed that the tumor cells of AFX were diffusely CD68-positive, and HMB-45 and Melan-A/MART1 expression was only limited to the large, multinucleated cells with vacuolated cytoplasm.