Multifocal Malignant Proliferating Trichilemmal Tumour: A Diagnostic Imitator Beyond the Scalp

Abstract

Malignant proliferating trichilemmal tumour (MPTT) is a rare cutaneous adnexal neoplasm arising from the outer root sheath of the hair follicle and represents malignant transformation of a proliferating trichilemmal tumour. It accounts for less than 0.1% of cutaneous malignancies and most commonly presents as a solitary scalp lesion in elderly women.
A 60-year-old male presented with progressively enlarging painful swellings over the scalp and left scapular region. Histopathological examination revealed a dermal epithelial tumour showing marked cytological atypia with abrupt trichilemmal keratinization. Periodic acid–Schiff staining demonstrated diastase-resistant cytoplasmic positivity. Immunohistochemistry showed focal CD34 expression with strong nuclear p53 and increased Ki-67 labeling index.
The findings were diagnostic of malignant proliferating trichilemmal tumour. Multifocal involvement occurring in a male patient is exceedingly rare. Recognition of trichilemmal keratinization and the use of histochemical and immunohistochemical markers are essential to distinguish MPTT from squamous cell carcinoma and guide appropriate management.