A Rare Occurrence of Sebaceous Carcinoma, Sebaceoma, Syringo
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Nevus sebaceous (NS) is a benign tumor with the potential to develop secondary benign and malignant neoplasms. It is a rare phenomenon to develop 2 or more skin tumors in a single NS lesion. A 62-year-old female patient presented with a history of the hairless patch over the right temporoparietal scalp since birth for which she never sought medical advice. She developed a mass on the top of this patch that had gradually enlarged over the last 6 months. Physical examination revealed a poorly defined 4 × 3-cm, erythematous orange-colored plaque extending from the right temporoparietal scalp to the temporal face. On top of this plaque, there was a single 1.5 × 1-cm yellowish dome-shaped eroded nodule.

The initial incisional biopsy from the yellowish nodule showed a malignant basaloid tumor with focal sebaceous differentiation and was diagnosed as sebaceous carcinoma. On immunohistochemistry, MLH-1, MSH-2, MSH-6, and PMS-2 showed intact nuclear expression. The lesion was then completely excised with 1-cm margins and was sent for histopathology examination. Microscopic examination of the formalin-fixed, paraffin-embedded, and hematoxylin- and eosin-stained tissue sections from the ulcerated nodule showed irregular lobules in the dermis composed mainly of basophilic pleomorphic cells with little cytoplasm and prominent nucleoli. Admixed rare foci of differentiated sebaceous cells were noted. Comedo-type necrosis and a large number of mitoses were also seen.

Immunohistochemical stains showed a positive reaction to adipophilin in the mature sebocytes and the tumor cells. EMA showed a positive reaction in the mature sebocytes. Ber-EP4 and CK20 showed a negative reaction. The diagnosis of poorly differentiated sebaceous carcinoma was confirmed on this portion of the tissue. Around this nodule, another basaloid tumor with peripheral palisading was seen with no evidence of clefting between the stroma and the tumor cells, and this tumor was diagnosed as trichoblastoma. Adjacent to trichoblastoma, there was another small superficial basaloid tumor with sebaceous differentiation but without peripheral palisading, mitoses, or necrosis, consistent with sebaceoma. Examination of more sections showed an invagination of the epidermis filled with papillae communicating with duct-like structures in the deep aspect of the lesion. These papillae were lined by an outer layer of tall columnar cells with the eosinophilic cytoplasm and an inner layer of cuboidal cells, and a diagnosis of SCAP was made for this lesion. The background skin showed hyperkeratosis, epidermal papillomatosis, and acanthosis. Several lobules of sebaceous glands communicated directly with the epidermal surface. Apocrine glands were also seen in the deep dermis. Based on these findings, the final diagnosis was poorly differentiated as sebaceous carcinoma, sebaceoma, trichoblastoma, and SCAP in a NS background. Completeness of excision was confirmed.