Syringocystadenocarcinoma papilliferum in situ is extremely rare. A 51-year-old female presented with a solitary yellowish patch on the scalp, accompanied by hair loss and a protruding mass. Histopathological evaluation revealed a large number of sebaceous glands and mild papillomatosis without hair follicles. The tumor contained many cystic spaces filled with amorphous material and a connection to the epidermis. The tumor cells showed papillomatous projections and were multilayered with nuclear atypia but no dermal involvement or lymphovascular invasion. On immunohistochemical analysis, the tumor cells showed immunopositivity for carcinoembryonic antigen, Ki-67, epithelial membrane antigen, and gross cystic disease fluid protein-15. Therefore, the patient was diagnosed with syringocystadenocarcinoma papilliferum in situ originating from a nevus sebaceus. The tumor was removed by wide excision, and no recurrence was observed. Our case report supports the multistep pathogenesis of syringocystadenocarcinoma papilliferum originating from a nevus sebaceus.

Background: Basal cell carcinoma (BCC) is the most common type of skin cancer. However, limited comparative data on the characteristics and prognosis of BCC in the H-zone and non-H-zone exist. Objective: We aimed to compare the clinical, histopathological, and surgical characteristics of BCCs in the head and neck region between the H- and non-H-zones. Methods: We retrospectively reviewed the clinical and histopathological characteristics of 292 head and neck BCC lesions in 275 patients and the characteristics of Mohs micrographic surgery (MMS) of 252 BCC lesions in 239 patients. Results: In the H-zone, 226 lesions (77.4%) were found. Clinically, patients with H-zone BCC, compared to those with non-H-zone, were significantly older (71.6±11.4 years vs. 64.6±13.5 years) and smaller in diameter (10.1±7.1 mm vs. 12.4±9.9 mm). The noduloulcerative type was more frequent in the H-zone, while the superficial and morpheaform types in the non-H-zone. Histopathologically, the infiltrative subtype was particularly noted in the H-zone than the non-H-zone (7.5% vs. 1.5%). Out of 37 BCC patients with prior treatment history, 31 (83.8%) were in the H-zone. Two out of 252 lesions (0.8%) recurred after MMS at our institution. The mean stages of MMS were comparable between the H- and non-H-zones (1.59 vs. 1.45, p=0.135). Conclusion H-zone BCCs were associated with older age and smaller tumor size compared to the non-H-zone BCCs. The noduloulcerative clinical and nodulocystic pathologic subtypes were the most common in both H-zone and non-H-zone BCCs.

Syringocystadenocarcinoma papilliferum in situ is extremely rare. A 51-year-old female presented with a solitary yellowish patch on the scalp, accompanied by hair loss and a protruding mass. Histopathological evaluation revealed a large number of sebaceous glands and mild papillomatosis without hair follicles. The tumor contained many cystic spaces filled with amorphous material and a connection to the epidermis. The tumor cells showed papillomatous projections and were multilayered with nuclear atypia but no dermal involvement or lymphovascular invasion. On immunohistochemical analysis, the tumor cells showed immunopositivity for carcinoembryonic antigen, Ki-67, epithelial membrane antigen, and gross cystic disease fluid protein-15. Therefore, the patient was diagnosed with syringocystadenocarcinoma papilliferum in situ originating from a nevus sebaceus. The tumor was removed by wide excision, and no recurrence was observed. Our case report supports the multistep pathogenesis of syringocystadenocarcinoma papilliferum originating from a nevus sebaceus.