Pilomatricoma is a benign cystic neoplasm characterized histopathologically by matrical differentiation.1 Clinically, pilomatricoma mainly presents in young individuals as a solitary cutaneous nodule with an average size of 1 cm and rarely exceeds 2 cm in diameter.1 Proliferating pilomatricoma is a recently described variant of pilomatricoma that usually presents as a solitary nodule measuring 1.5-5.5 cm in diameter and histologically composed of a large lobular proliferation of basaloid cells in association with small foci of shadow cells.2 Very few cases of proliferating pilomatricoma have been described in the literature, and all the cases that have been described have presentation in the elderly around the seventh decade of life.3-6 Here, we report a case of an 18-year-old woman with proliferating pilomatricoma.
An 18-year-old woman presented with a 2-month history of a painless mass on the right cheek and no history of trauma to the site. Physical examination revealed a firm reddish nodule, 1.8 × 1.5 cm in diameter with a shiny surface, on the right cheek (Fig. 1). The possible diagnosis of pilomatricoma and pyogenic granuloma was made. The lesion was excised with a 2-mm margin, and the defect was closed primarily. Biopsy specimens from the patient's cheek revealed lobular proliferation of basaloid cells containing small foci of shadow cells. The tumor was predominantly composed of basaloid cells with a large number of mitotic figures (Fig. 2). The typical histological feature led to the diagnosis of proliferating pilomatricoma. No evidence of recurrence was observed 8 months later (Fig. 1).
Proliferating pilomatricoma was first described by Kaddu et al3 in 1997 as a histopathologically distinctive subset of pilomatricoma. To date, 13 patients have been described in 4 reports of proliferating pilomatricoma, ranging in age from 42 to 88 years (mean age: 66.5 years).3-6 The lesions in the reports were situated mostly on the head and neck. The histological features of proliferating pilomatricoma are characterized by a lobular proliferation composed mainly of basaloid cells, in association with focal areas containing eosinophilic “shadow” cells.2 The basaloid cells show variable nuclear atypia and several mitotic figures, ranging from 4 to 15 per high-power field.2
Proliferating pilomatricoma represents a distinctive histopathological entity that should be differentiated from other benign and malignant neoplasms with hair matrical differentiation. The differential diagnosis includes classical pilomatricoma, pilomatrical carcinoma, and basal cell carcinoma with matrical differentiation. Fully developed classical pilomatricomas present a single cystic character with large zones of eosinophilic material containing shadow cells and only small areas of basaloid cells, which are arranged mostly along the periphery.7 Pilomatrical carcinoma presents a relatively large, asymmetrical, poorly circumscribed lesion composed of several basaloid aggregations with prominent atypia and numerous mitotic figures.7 Pilomatrical carcinoma may also present features suggestive of lymphatic or perineural invasion.7 Basal cell carcinoma with matrical differentiation usually exhibits basaloid aggregates, which often connect to the epidermis, and retraction spaces between the lobules and stroma.7
Whether proliferating pilomatricoma is a precursor of pilomatrical carcinoma is not currently known.3 Therefore, all these neoplasms should be excised with adequate surgical margins, and careful follow-up examinations are strongly recommended.5
Our case is the first report of proliferating pilomatricoma observed in a patient of young age. Proliferating pilomatricoma can occur at younger ages and should be considered in the differential diagnosis of solitary lesions in adults and children, even if the lesion is rapidly growing.
Ji-Won Byun, MD
Chan-Yl Bang, MD
Bo-Hee Yang, MD
Hee-Jin Song, MD
Hyeon-Sook Lee, MD, PhD
Jeong-Hyun Shin, MD, PhD
Gwang-Seong Choi, MD, PhD
Department of Dermatology INHA University School of Medicine, Incheon, South Korea
1. Kaddu S, Soyer HP, Hödl S, et al. Morphological stages of pilomatricoma. Am J Dermatopathol
2. Marrogi AJ, Wick MR, Dehner LP. Pilomatrical neoplasms in children and young adults. Am J Dermatopathol
3. Kaddu S, Soyer HP, Wolf IH, et al. Proliferating pilomatricoma. A histopathologic simulator of matrical carcinoma. J Cutan Pathol
4. Hague JS, Maheshwari M, Ryatt KS, et al. Proliferating pilomatricoma mimicking pyogenic granuloma. J Eur Acad Dermatol
5. Sakai A, Maruyama Y, Hayashi A. Proliferating pilomatricoma: a subset of pilomatricoma. J Plast Reconstr Aesthet Surg
6. Niiyama S, Amoh Y, Saito N, et al. Proliferating pilomatricoma. Eur J Dermatol
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7. Hardisson D, Linares MD, Cuevas-Santos J, et al. Pilomatrix carcinoma: a clinicopathologic study of six cases and review of the literature. Am J Dermatopathol