Cutaneous Neoplasms with Sebaceous Differentiation: A Comprehensive Update on Clinical, Histopathological and Molecular Classification.

Cutaneous sebaceous neoplasms are rare adnexal tumours differentiated towards sebaceous glands, spanning a biological spectrum from benign (sebaceous adenoma, sebaceoma, nevus sebaceus) to outright malignant (sebaceous carcinoma). Most tumours are sporadic and solitary, with a predilection for the head and neck of elderly adults, but a clinically important subset is observed in the setting of Lynch syndrome/Muir-Torre syndrome. Recent large-scale genomic and transcriptomic studies have provided insights into the pathogenesis of these unique neoplasms, revealing a genetically heterogeneous landscape shaped by mismatch repair deficiency, UV damage, and abnormalities in several other key signalling pathways. The inclusion of nevus sebaceus within the sebaceous tumour family in the WHO 5th Edition of Skin Tumours reflects a conceptual shift, recognising nevus sebaceus as a clonal, mutation-driven neoplasm and a precursor lesion for secondary tumour development.