Track

Abstract

Sebaceoma is a benign adnexal neoplasm with sebaceous differentiation, typically composed of immature basaloid cells and variable mature sebocytes. While some arise in the setting of mismatch repair deficiency, recent studies have identified recurrent GRHL fusions in a molecularly distinct subset. The full clinicopathologic spectrum of these tumors remains incompletely characterized. We report three sebaceomas with confirmed GRHL fusions. Patients were men aged 40-84 years. Tumors arose on the lip, cheek, and axilla and measured 1-3 cm. All were well-circumscribed dermal nodules composed of predominantly immature basaloid cells and scattered mature sebocytes. Two displayed rippled or organoid architecture; the third showed scattered infundibular cysts with only rare mature sebocytes evident on biopsy. Androgen receptor was diffusely positive in both tested cases. Whole transcriptome RNA sequencing identified RCOR1::GRHL2 fusions in all tumors, with identical breakpoints (exons 11 and 3). The axillary lesion represents, to our knowledge, the first reported GRHL-rearranged sebaceoma outside the head and neck. These findings expand the known anatomic range and highlight the diverse morphologic spectrum of GRHL-rearranged sebaceomas. Recognition may be challenging, particularly in tumors with scant mature sebocytes or prominent infundibulocystic features, leading to potential misclassification. Awareness of this entity and the use of targeted fusion testing can aid accurate diagnosis in such cases.