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Abstract

Tumor of follicular infundibulum (TFI) is a rare cutaneous neoplasm of unclear histogenesis. Various benign and malignant cutaneous neoplasms have been reported in association with TFI, including most commonly basal cell carcinoma (BCC). Some authors have suggested that TFI may represent a variant of BCC. However, to our knowledge, no previous studies investigating the molecular pathogenesis of TFI have been reported. Herein we present next-generation DNA sequencing results of four cases of TFI. Four skin biopsies associated with a final diagnosis of tumor of follicular infundibulum from 2000-2024 were identified by searching the pathology laboratory information system of a single academic hospital. Three of the 4 patients were male, and the mean age at diagnosis was 57.8 years (range: 46-68 years). All four tumors were located on the face. Clinically, two tumors demonstrated features suggestive of basal cell carcinoma, and two presented as an eruption of multiple hypopigmented lesions. Molecular profiling of formalin-fixed paraffin-embedded tissue from each tumor was performed using the OncoPanel next-generation DNA sequencing platform. In total, 18 unique mutations in 15 genes spanning an array of cellular functions including DNA repair and cell signaling were identified. No mutations in Hedgehog signaling pathway genes were observed. Three cases demonstrated SLX4 mutations. Absence of mutations in Hedgehog pathway genes in all cases of TFI strongly suggests it is a separate entity from BCC. The significance of SLX4 mutations identified in the majority of cases is unclear and warrants further investigation.