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Rare Cancer Presentations
Published in Debjani Sahni, Adam Lerner, Bilal Fawaz, Advanced Skin Cancer, 2022
Bilal Fawaz, Heather A. Edwards, Monica Rosales Santillan, Debjani Sahni, Connor O’Boyle, Daniel L. Faden
Trichilemmal cyst (TC), also known as pilar cyst, is a common, benign cyst originating from the outer root sheath of the hair follicle. Proliferating trichilemmal tumor (PTT) and its malignant counterpart MPTT are thought to arise from TC and are exceedingly rare.1 The three neoplasms lie on a continuum with progressively worsening clinical behavior, histologic atypia, and architectural disorder.2,3
Benign tumors
Published in Archana Singal, Shekhar Neema, Piyush Kumar, Nail Disorders, 2019
This is an exceedingly rare tumor of the nail bed with insidious symptomless growth. It resembles a wart, Bowen’s disease, or SCC; its very slow progression and absence of pain distinguishes it from KA. Histopathology shows a lesion morphologically very similar to proliferating trichilemmal cyst, hence its designation. It appears solid and mainly exophytic, though many small and medium-sized cyst-like formations are seen. The peripheral cells are relatively small with dense nuclei. Towards the center of the neoplasm, the cells increase in size to finally keratinize abruptly without a granular layer (Figure 26.21).
Epithelial and fibroepithelial tumors
Published in Eckart Haneke, Histopathology of the NailOnychopathology, 2017
Proliferating onycholemmal cyst is morphologically very similar to proliferating trichilemmal cyst, hence its designation. It appears solid and mainly exophytic, though many small and medium-sized cyst-like formations are seen. The peripheral cells are relatively small with dense nuclei, but their arrangement is not as regular as in a trichilemmal cyst. Toward the center of the tumor formations, the cells increase in size to finally keratinize abruptly without a granular layer. Again, the keratin is not as regular as in a trichilemmal cyst and often has the appearance as if it were rather the result of keratinocyte necrosis than of regular keratinization. Long slender digitiform epithelial extensions are seen between the tumor islands (Figure 8.17).
Squamous cell carcinoma arising in an epidermal inclusion cyst
Published in Baylor University Medical Center Proceedings, 2022
Suzanne Alkul, Christopher N. Nguyen, Nisha S. Ramani, Mahmud Alkul, Ida Orengo, Ikue Shimizu, Bhuvaneswari Krishnan
The pathologic differential diagnostic considerations of a dermal cystic lesion lined by squamous epithelium include an inclusion cyst of epidermal or pilar type. The epidermal type shows squamous lining epithelium with preserved granular layer and lumen with epidermal-type keratinous material. The pilar type cyst epithelium shows squamous cells with absence of granular layer, and lumen with eosinophilic pilar-type keratinous material with cholesterol clefts/calcification. Squamous lined cysts secondary to human papillomavirus infection have been reported18–20 and are more commonly on the palms and soles and rarely the scalp. These cysts show squamous lining epithelia with papillomatosis, hypergranulosis, parakeratosis, and, rarely, cytoplasmic inclusions. Proliferative changes in the cyst wall occupying the cyst lumen can be seen in proliferating trichilemmal or epidermal cysts, or malignancy arising in epithelial cysts. Proliferating trichilemmal tumors, commonly seen in the scalp, show a wide spectrum of squamous proliferation. Epithelial proliferation with pleomorphism and surrounding stromal invasion is seen in carcinomas arising in trichilemmal cyst. A proliferating epidermal cyst shows squamous proliferation with epidermal-type keratinization. Atypia of the squamous cells can be seen.