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Basaloid follicular hamartoma is a benign lesion of important consideration because it can be mistaken both clinically and histologically for basal cell carcinoma. The formation of basaloid follicular hamartoma has been linked to a mutation in the patched gene, which is part of the same pathway implicated in nevoid basal cell carcinoma syndrome. While these hamartomas are considered benign lesions, malignant growths have been reported to arise within them, which raises the question, "Is basaloid follicular hamartoma a premalignant lesion?" Correct identification allows for periodic monitoring for malignant transformation, while sparing patients unnecessary surgery. Treatment strategies, including experimental therapies, are reviewed.
(Arch Pathol Lab Med. 2010;134:1215-1219)
Basaloid follicular hamartoma (BFH) is a rare, benign, superficial malformation of hair follicles that presents histologically as an epithelial proliferation of basaloid cells and clinically in various forms, with and without associated diseases.
This entity was first described in 1969 by Brown et al1 as multiple papules in the nasolabial folds associated with myasthenia gravis and diffuse alopecia (Brown-Crounse syndrome). In 1985, the term basaloid follicular hamartoma was coined by Mehregan and Baker,2 who reported a localized and solitary type of lesion without associated abnormalities. Recently, Morohashi et al3 described BFH as an abortive growth of secondary hair germs with a limited differentiation toward the upper follicular portion.
PATHOGENESIS
Genetic studies have linked BFH to a mutation in the patched (PTCH) gene on chromosome band 9q23. The gene is part of the same pathway implicated in nevoid basal cell carcinoma syndrome (NBCCS) or Gorlin-Goltz syndrome, though its expression is less severe.4,5 The PTCH gene encodes a receptor for the protein product of the sonic hedgehog gene (SHH), a member of the hedgehog family of genes that are involved in developmental patterning during embryonic development. The PTCH receptor forms a receptor complex with another transmembrane protein known as SMO (for "smoothened"). When SHH protein is absent, PTCH receptor inactivates SMO and keeps it from transducing a downstream signal. Binding of SHH protein to the PTCH receptor releases the suppression of SMO, causing the upregulation of hedgehog target genes through a signal cascade that involves transcription factors in the Gli family.6,7 Unregulated signaling can lead to increased cell division resulting in abnormal growth and abnormal patterning.8
Mutations in this pathway...