Abstract

Primary cutaneous adnexal carcinomas are exceedingly rare in pediatric patients. To the best of our knowledge, we describe a new entity.

We report a 12-year-old female with a growing, tender lesion present since birth. A 1.5 cm violaceous subcutaneous nodule on the buttock was excised. The histopathologic findings revealed large nodular aggregates with a sieve-like pattern of atypical basaloid tumor cells with microcystic change, clear cell change containing scant trichohyaline granules, and extensive necrosis in a background of fibromucinous stroma and multifocal calcification. The cells stained positively for p63, AE1/AE3 (weak and patchy), β-Catenin (nonspecific cytoplasmic), and focal EMA, and negatively for CK7, CK20, CD117, SOX-10, and Ber-Ep4. DNA panel and whole transcriptome sequencing were negative for pathogenic mutations, copy number changes, or gene fusions. In accordance with expert consultation, the findings are most suggestive of a low-grade adnexal carcinoma with a cribriform pattern.

The differential diagnosis includes basal cell carcinoma, adenoid cystic carcinoma, and trichoblastoma which are less likely given the patient’s young age, sun protected site, and lack of Ber-EP4 expression, negative SOX-10 and CD117 expression, and lack of intratumoral CK20 positive cells, respectively. The presence of trichohyaline granules and non-specific β-Catenin staining raises the possibility of matrical lineage. The biologic potential of this tumor is unknown, although the morphologically similar primary cutaneous cribriform carcinoma follows an indolent course, with no recurrence or metastasis reported. In addition, it is important to exclude metastatic tumors from the breast, salivary gland, and gastrointestinal tract that show similar cribriform pattern histologically.