Answer of Dermatopathology Case 91

Proliferating Trichilemmal Cyst (Pilar Tumour)

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Abstract:

Proliferating trichilemmal tumors: a review of the literature. Dermatol Surg. 2007 Sep;33(9):1102-8.

BACKGROUND: Proliferating trichilemmal tumors (PTTs) are uncommon lesions whose histologic hallmark is the presence of trichilemmal keratinization. PTT is thought to originate from the trichilemmal cyst (TC) and have the potential for malignant transformation, at which point it is termed a malignant proliferating trichilemmal tumor (MPTT). These lesions may cause considerable morbidity and even mortality, and recurrence after simple local excision is common.
OBJECTIVE: The objective was to review the clinical presentation, histopathologic characteristics, malignant potential, and treatment options for PTT.
METHODS: The English literature was reviewed regarding PTT, TC, and MPTT.
RESULTS: PTT generally presents as a subepidermal tumor on the scalp in women over the age of 60. Histologic findings may be used to differentiate PTT from TC and MPTT. Complete surgical excision is recommended; additional radiotherapy and/or chemotherapy may be used for lesions with increased invasive potential.
CONCLUSION: Adequate treatment of PTT requires skilled histopathologic examination for proper diagnosis; histologic appearance may not correlate with clinical behavior. After surgical excision, long-term clinical follow-up for evidence of metastatic disease is judicious.

Proliferating trichilemmal tumors: clinicopathologic evaluation is a guide to biologic behavior.J Cutan Pathol. 2003 Sep;30(8):492-8.

BACKGROUND: Trichilemmal (pilar) cysts are common skin lesions that usually occur on the scalp of elderly women. They differentiate towards the follicular outer root sheath epithelium and show trichilemmal keratinization. Proliferating trichilemmal tumor (PTT) shows features of typical pilar cyst, but additionally shows extensive epithelial proliferation, variable cytologic atypia and mitotic activity. The malignant potential of PTT is controversial, as only a small number of histologically malignant PTTs and a smaller number of clinically malignant PTTs have been reported.
METHODS: We retrieved from our archives five PTTs that deviated from ordinary PTTs with regards to either cytology or architecture. We also reviewed all previous reports of histologically malignant PTTs, with the goal of delineating criteria for the diagnosis of malignant PTTs.
RESULTS: Five cases of PTT showing atypical cytoarchitectural features were retrieved from our archives and reviewed with respect to size, growth pattern, cellularity, cytologic atypia, and mitotic activity. The patients (four female, one male) ranged from 54 to 83 (mean 65) years. The tumors measured from 1 to 16 cm in diameter (mean 5 cm) and four out of five occurred on the scalp. All tumors showed at least focal areas of typical PTTs. Three cases were circumscribed but had areas of moderate to focally marked cytologic atypia. Two cases showed infiltrative growth, marked cytologic atypia and mitotic activity. Clinical follow-up was available for four of five cases and ranged from 6 to 84 (median 48) months. Follow-up showed two cases with local recurrence and one case with distant metastasis. This last patient died of disease; all other patients are disease-free.
CONCLUSIONS: Review of our cases and the published literature suggests that the diagnosis of malignant PTT be given to PTT showing a combination of non-scalp location, recent rapid growth, size greater than 5 cm, infiltrative growth, and significant cytologic atypia with mitotic activity. At the present time the stratification of malignant PTT into low- and high-grade categories is not possible.

Proliferating trichilemmal cyst with focal invasion: report of a case and a review of the literature. Am J Dermatopathol. 2000 Apr;22(2):183-7.

Proliferating trichilemmal cyst (PTC) is a rare but morphologically distinctive tumor that usually occurs in the scalp of elderly women. Furthermore, only 30 well-documented examples of so-called malignant PTC have been reported. Alternatively, some authors have recently proposed that PTC is squamous cell carcinoma. We describe a case of PTC with focal invasion that was indistinguishable from squamous cell carcinoma in areas, and we review the literature. This debate should be considered in PTCs to provide adequate treatment (wide local excision) and follow-up (long term), particularly in large and long-standing lesions.