After an extensive literature search, this is the first reported case of pilomatrixoma of the breast in Oman. We share this rare case with a brief review of the currently available literature.

Case Report

A 51-year-old man with no comorbidities presented with six months of swelling on his right breast. Though the swelling did not increase in size over time, it was associated with pricking pain. No nipple discharge was noted. There was no history of trauma. Family history revealed that his mother had breast cancer.

On examination, both breasts looked symmetrical with normal nipple-areolar complex. A small nontender, hard 2.0 × 1.0 cm lump was noted at two o’clock in the right breast attached to unremarkable skin. Mammography showed a well-defined dense lesion on the medial aspect of the periareolar region measuring 1.6 × 1.0 cm with peripheral microcalcifications [Figure 1]. Ultrasound of the right breast also confirmed the presence of a well-defined homogeneous, hypoechoic, subcutaneous oval lesion of similar dimensions located 0.5 cm from the nipple [Figure 2]. The lesion was excised under local anesthesia in thebreast clinic.

The resected specimen was subjected to histopathological examination. Grossly, it was a well-circumscribed, firm, oval nodule measuring 2.0 × 1.7 × 1.7 cm with an overlying ellipse of skin measuring 1.8 × 0.6 cm [Figure 3]. On slicing, the nodule showed a solid, yellow, and gritty cut surface due to areas of calcification. Microscopic examination revealed a neoplasm in the dermis composed of solid nests of basaloid cells undergoing abrupt trichilemmal-type keratinization resulting in eosinophilic ‘shadow’ or ‘ghost cells’ [Figure 4]. Also noted in the stroma were scattered foci of calcification with foreign body reaction and infiltration by chronic inflammatory cells [Figures 5 and 6]. These findings were consistent with pilomatrixoma. When the patient visited the clinic 10 days after the excision, his wound had healed well. He was reassured that the lesion was benign and completely excised.

Discussion

Pilomatrixoma, also known as pilomatricoma or ‘calcifying epithelioma of Malherbe’ was first recognized in 1880 by Malherbe and Chenanatais.1 It is a rare, slow-growing benign neoplasm originating from the hair matrix, more common in children and young adults with a slight female preponderance.2 While pilomatrixoma can develop in any hair-bearing skin, it is most commonly seen in the head and neck regions. Less commonly, they are noted in the upper extremities, trunk, and lower extremities.3 Pilomatrixoma’s appearance in the breast is considered rare (1:100 000 people). After an extensive literature search, we found nine cases of pilomatrixoma of the breast in adult males reported in the English language [Table 1].

These tumors are usually sporadic but around 75% of the cases have mutations in the CTNNB1 gene (which regulates beta-catenin), thereby triggering quick, uncontrolled division of matrix cells leading to pilomatrixoma. Some cases were also found to be related to Gardner syndrome and myotonic dystrophy.12 The exact pathogenesis of pilomatrixoma is still unclear, however, some suggest that recurrent skin trauma induces an inflammatory response leading to hair matrix overgrowth while others consider them to be hamartomas.11 It usually presents as an asymptomatic, single, subcutaneous, firm nodule attached to the skin, sized 1–3 cm. Rarely, they may grow > 5 cm (giant pilomatrixoma). Some of these lesions may be associated with red-blue discoloration of the skin and ulceration.13

Mammography commonly demonstrates a dense mass with multiple, irregular, pleomorphic microcalcifications.10 In addition, Sonography may show a well-circumscribed, oval mass with internal echogenic foci and a peripheral hypoechoic rim, as it did in the present case. If these lesions get calcified, they would appear as hyperechoic masses with posterior acoustic shadowing.

Although imaging studies are useful in determining the size and location of the lesion, core needle biopsy is the modality of choice for confirmation of diagnosis. Histopathological features typically consist of two types of cells surrounded by foreign-body giant cells and calcifications. These are ‘shadow’ or ‘ghost’ cells which are located centrally and basophilic cells at the periphery.10

Pilomatrixomas are benign and the tendency to develop into malignancy is extremely rare with very few reported cases of pilomatrix carcinoma. The majority of the literature agrees on surgical excision as the treatment of choice.9 It serves the cosmetic purpose and prevents the rare possibility of malignant transformation of the tumor. On the other hand, some suggest a conservative approach for patients with a small superficial breast mass showing benign imaging characteristics. These include masses of breast imaging-reporting and data system category 3 without pathologic diagnosis or benign biopsy results.3

Conclusion

Pilomatrixoma in the male breast is a rare benign lesion. It can mimic breast carcinoma because of associated calcification. Therefore, it is prudent to consider pilomatrixoma as a differential diagnosis in patients presenting with superficially located breast lumps.

Disclosure

The authors declared no conflicts of interest. A written consent was obtained from the pateint.

references

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