Giant pilomatricoma with coexisting angiomyxoid stroma histopathology: a case report

Pilomatricoma, also known as benign calcifying epithelioma of Malherbe, is a follicular tumor originating from cells in the hair follicle matrix. It usually manifests as a firm subcutaneous mass up to 3 cm in size. Less commonly, it may measure >5 cm and in such cases is called giant pilomatricoma. We herein present a case of a subcutaneous lesion that was characterized by aggressive biological behavior and initially thought to be malignant but subsequently found to be a rare angiomyxoid variant of giant pilomatricoma. This case involved a young, healthy woman with a rapidly growing subcutaneous lesion on the distal lateral side of her right arm. An incisional biopsy was performed, and the lesion was diagnosed as hyperplasia of the epidermis and subcutaneous tissue, likely of reactive nature. After radical excision, analysis of the entire specimen led the pathologist to diagnose a rare variant of giant pilomatricoma with angiomyxoid stroma. Classic pilomatricoma is an indolent, slow-growing lesion that is well defined and not fixed to the underlying tissue planes. However, after showing no signs of enlargement for 6 months, the lesion in the present case began to grow in a very unusual and concerning manner, suggesting a skin malignancy. The patient’s young age and the rapid development and large dimensions of the lesion led us to suspect a sarcoma. This case highlights the importance of cooperation between the dermatosurgeon and the pathologist to ensure thorough evaluation of such misleading cases. Such cooperation will guide appropriate management decisions and avoid overtreatment of benign lesions.