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A 54-year-old man presented with a recurrent swelling on the right occipital region of the scalp. Two months earlier, the patient had undergone an initial local excision of the lesion which had enlarged progressively over the previous 2 years on a hairless patch which had been present since birth. On examination, a 5 × 4-cm, pinkish, firm, ulcerated swelling was seen on the right occipital region with a scar running over it. The lesion was not fixed to the underlying bone and there was no regional lymphadenopathy. X-Ray of the skull was normal and no evidence of metastatic disease was identified. Wide local excision of the tumor was performed and it was sent for histopathologic examination. Specimens and slides of the earlier surgery performed elsewhere were also studied.

The specimen of the initial surgery consisted of skin-covered tissue with an exophytic firm growth measuring 6 × 5 × 4 cm. The skin surface was rough with areas of ulceration. No necrosis was noted grossly. Microscopically, three distinct lesions were seen. One was a well-circumscribed tumor located in the superficial dermis with lobules of basaloid cell aggregates with peripheral palisading and with no epidermal connection. The lobules were surrounded by cellular fibrous tissue (Fig. 1). Unlike basal cell carcinoma, however, no cleft between the cellular aggregates and stroma was noted. Foci of pigmentation were seen within cellular lobules and these features were consistent with a diagnosis of trichoblastoma. The second tumor was seen adjacent to the first, and consisted of duct-like structures and cystic spaces with papillary projections. These were lined by double-layered epithelium with stromal infiltration by plasma cells, which are features of syringocystadenoma papilliferum (Fig. 2). The third lesion was a spindle cell sarcoma which formed the major part of the lesion, diffusely infiltrating the dermis and subcutaneous tissue, elevating and ulcerating the overlying skin. The tumor consisted of interlacing fascicles of spindle cells with oval to elongated nuclei having finely dispersed chromatin and inconspicuous nucleoli. The tumor cells were seen encircling the sweat glands, without destroying them (Fig. 3). Nuclear pleomorphism was minimal, with a mitotic rate of 9–10 per high-power field. A small area of epidermal hyperplasia with acanthosis and papillomatosis overlying malformed highly placed sebaceous glands was the only evidence of a pre-existing nevus sebaceus. The status of the surgical margins was not clearly discernible.

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Figure 1. Trichoblastoma with lobules of basaloid cells, papillary formation of syringocystadenoma papilliferum, and spindle cells of cutaneous leiomyosarcoma (hematoxylin and eosin, ×40)

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Figure 2. Higher power shows syringocystadenoma papilliferum lined by double-layered epithelium and spindle cells of cutaneous leiomyosarcoma. Trichoblastoma is seen in the left lower corner (hematoxylin and eosin, ×100)

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Figure 3. Malignant spindle cells encircling sweat glands (hematoxylin and eosin, ×100)

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The wide excision specimen of the recurrent swelling consisted of a skin-covered nodule with ulceration, measuring 3 × 4 × 3 cm, with a gray–white whorled cut surface. No necrosis was noted grossly. Multiple sections showed only spindle cell sarcoma infiltrating the skin and subcutaneous tissue, morphologically similar to the earlier tumor, with ulceration of the overlying skin. The surgical margins were free from tumor.

Immunohistochemical stains on the spindle cell sarcoma showed positive staining for smooth muscle actin (SMA) (Fig. 4), vimentin, epithelial membrane antigen (EMA), and S100. The tumor cells were negative for cytokeratin (CK), HMB45, desmin, glial fibrillary acidic protein (GFAP), CD34, and CD68. Correlating the histomorphology and immunohistochemical findings, a diagnosis of cutaneous leiomyosarcoma with trichoblastoma and syringocystadenoma papilliferum arising on nevus sebaceus was made.

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Figure 4. Immunoperoxidase stain shows strong expression of smooth muscle actin in malignant spindle cells (ABC technique, ×400)

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The patient received postoperative radiotherapy and is disease free 8 months after diagnosis.