Abstract
Proliferating trichilemmal tumours (PTT) are defined by a benign squamous cell proliferation inside a trichilemmal cystic (TC) cavity. A possible explanation of this proliferative phenomenon within the cyst may be molecular alterations in genes associated to cell proliferation, which can be induced by ultraviolet radiation. Among other genes, alterations on TP53 and DNA mismatch repair proteins (MMR) may be involved in the cellular proliferation observed in PTT. Based on this assumption, but also taking into account the close relationship between the sebaceous ducts and the external root sheath where TC develop, a MMR, a p53 expression assessment and a TP53 study were performed in a series of 5 PTT cases, including a giant one. We failed to demonstrate a MMR disorder on studied PTT, but we agree with previous results suggesting increased p53 expression in these tumours, particularly in proliferative areas. TP53 alteration was confirmed with FISH technique, demonstrating TP53 deletion in most cells.
Highlights
Trichilemmal cyst (TC) is a benign cyst derived from the external root sheath of the catagen hair follicle isthmus by a budding-off mechanism [1]
A mutation on these genes is constitutively present in the cells of Lynch syndrome patients, and in its variant associated with cutaneous sebaceous neoplasms, Muir-Torre syndrome [25,26]
The studied tumours showed a well-defined cystic architecture, with several prolifprobe specific for the TP53 gene located in chromosome 17p13 and another directed to the erative changes and a trichilemmal squamous lining (Figure 2)
Summary
Trichilemmal cyst (TC) is a benign cyst derived from the external root sheath of the catagen hair follicle isthmus by a budding-off mechanism [1]. A mutation on these genes is constitutively present in the cells of Lynch syndrome patients, and in its variant associated with cutaneous sebaceous neoplasms, Muir-Torre syndrome [25,26]. This mutation is present in other carcinomas including up to 15% of sporadic colorectal adenocarcinomas [24,27]. Other cutaneous tumours where the role of MMR proteins has been studied are melanocytic tumours [34], squamous neoplasms [35] and even simple TC [36], showing reduced expression in melanocytic lesions and no evidence of mutation in squamous carcinoma or trichilemmal cysts. We wanted to search for alterations in the IHQ the IHQ expression of p53 and MMR proteins, looking for deletion of TP53 in these expression of p53 and MMR proteins, looking for deletion of TP53 in these tumours tumours via a FISH assay, in antoattempt explain their proliferating via a FISH assay, in an attempt explaintotheir proliferating nature. nature
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