Introduction: Malignant proliferating trichilemmal tumour (MPTT) is a rare neoplasm with less than 50 cases documented in the literature. It is more common on the scalp and in females. We report a case of MPTT and review the histopathology, differential diagnoses and management.
Case report: An 84-year-old male presented with a tan subcutaneous scalp nodule and underwent an elliptical skin excision (30×22×15 mm). Histopathology showed a well circumscribed dermal mass with a multi-loculated cystic appearance. It was lined by squamous epithelium with an absent granular layer showing evidence of abrupt keratinisation. The keratinocytes showed marked cytologic atypia. Numerous mitoses including atypical mitotic figures were seen. The lesion extended to the margins. The morphological features were consistent with a MPTT.
Discussion: It is important to recognise this rare entity as MPTT tends to recur and metastasise more frequently than the histological mimics of squamous cell carcinoma (SCC) and trichilemmal carcinoma (TLC). Features favouring MPTT over SCC include presence of trichilemmal type keratinisation and the lack of a premalignant epidermal lesion. TLC is distinguished by a lobular proliferation of clear cells and continuity with the epidermis. Wide excision of MPTT with an adequate clearance margin and close follow up are the mainstays of treatment.
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