Pilomatrixoma with Atypical Features: A Case Report

Abstract

Pilomatrixoma is an uncommon, benign tumor with differentiation towards both the hair matrix and cells arising in the cortex, most frequently appearing in the first or second decade of life. In rare instances, pilomatrixomas can show malignant transformation. Pilomatrix carcinoma is extremely uncommon and has traditionally been considered a tumor of low malignant potential; however, a high local recurrence rate has been reported. There is a paucity of literature on these lesions, with only a few reports describing the spectrum of malignant changes seen in these lesions. In this case report, we present a case of pilomatrixoma in an adult patient showing atypical features. While the tumor is small, there are focal features that suggest progression to malignancy, but do not fulfill the criteria for pilomatrix carcinoma. These focal atypical features include a focal infiltrative pattern at the periphery, with a variable cytological atypia and an increased mitotic rate, up to five mitotic events/high-power field. Irregular foci of central necrosis (comedonecrosis) were present in several lobules. Some of the features identified were similar to a subset of pilomatrixoma, known as “proliferating pilomatrixoma.” However, our case did not have the diffuse changes or larger size that has been frequently reported in “proliferating pilomatrixoma.” In conclusion, given the lack of focality of the changes, the lesion in our case is best described as a pilomatricoma with atypical features. Furthermore, our case may highlight the need to ensure close clinical follow-up for these lesions with unexpected atypical features that raise concern of recurrence and malignant transformation.

Pilomatrix Carcinoma in a 4-Year Old Child With an Unusual Presentation

“…However, due to its rarity differentiating histologic features from pilomatrix carcinoma are not well defined and lacks standardization. 7 Most of the reported cases of proliferating pilomatrixoma exhibited a focal infiltrative pattern, foci of comedonecrosis, variable nuclear atypia and increased mitotic activity. None of these cases showed vascular or lymphatic invasion.…”

“…None of these cases showed vascular or lymphatic invasion. 7 It is important to recognize this variant due to its potential for local recurrence compared to conventional or benign pilomatrixoma. Moreover these intermediate neoplasms have low metastatic potential, therefore differentiation from other malignant tumours such as basal cell carcinoma and pilomatrix carcinoma is important.…”

Commonly Misdiagnosed Facial Lesion: Pilomatricoma

“…It is slightly more common in female (7,8). The common locations of Pilomatricoma were the head and neck, upper extremities, trunk, and lower extremities (2)(3)(4). In addition to that, 40% of them were discovered on the head, particularly in the cheek or palpebral area (4, 7).…”

“…Malherbe and Chenantais, in 1880 described a benign skin lesion which was called the calcifying epithelioma (1). Forbis and Helwig later discovered through histopathological examination that the lesion originated from the matrix cells of hair follicles (2,3). Since then, this benign lesion was referred to as "Pilomatricoma" or "Pilomatrixoma", which typically manifest in the first or second decade of life.…”

Pilomatrixoma Pathology Description of Squamous Cell Carcinoma: A Case Report

“…Dystrophic calcification begins in ghost cells in the form of fine granules. 3 The tumor is often cystic and may rupture. Ghost cells can be destroyed by the giant cell reaction.…”