Abstract
Sebaceous carcinoma is a rare malignant epithelial tumor histologically characterized by cells differentiating into sebaceous glands. Sebaceous carcinoma predominantly occurs in elderly patients on the head and neck, particularly on the eyelids.
We report two cases of sebaceous carcinoma occurring in the inguinal region. Case 1: A 50-year-old Japanese man had 1-year history of a reddish tumor in his right inguinal region. This tumor has grown to erosive red-colored tumor （approximately 60×40 mm in size）. Case 2: A 77-year-old Japanese woman had 20-year history of a slow-growing cutaneous tumor in her left inguinal region. The tumor has changed into an ulcerated reddish-brown nodule （27×15 mm in size）. The both tumors were radically extirpated. Histopathological examination of excised specimens revealed atypical cells with foamy cytoplasm in the center and atypical cells with flat nuclei at the tumor nest margins, indicating sebaceous differentiation. On immunohistochemical examination, tumor cells showed immunopositivity for epithelial membrane antigen （EMA） and immunonegativity for Ber-EP4 （anti-CD326 antibody）. Additionally, adipophilin-positive cells were observed in some areas of the tumor nests. Based on these findings, both specimens were diagnosed with sebaceous carcinoma. The final diagnosis was a well-differentiated sebaceous carcinoma in Case 1, whereas it was poorly-differentiated sebaceous carcinoma, primarily composed of squamoid cells in Case 2.
The differential diagnosis usually includes basal or squamous cell carcinoma in patients with this presentation; therefore, immunohistochemical evaluation for EMA, Ber-EP4, and adipophilin expression is essential, especially in case of poorly differentiated sebaceous carcinoma, as was observed in Case 2.
Sebaceous carcinoma is rare in the inguinal region, which is attributable to the low level of ultraviolet light exposure in this area. Further studies would be necessary to clarify the tumorigenesis of sebaceous carcinoma in the inguinal region.
