Common tumor in an uncommon location: Pleomorphic adenoma of the breast

A 64-year-old female with no personal or family history of breast cancer, presented with a mobile, elastic and hard retro-areolar mass of the right breast, that gradually increased in size. No fever was noted. There was no history of trauma. No changes involving the skin and no axillary lymphadenopathy were noted.

Mammography of the right breast (Fig 1) showed a 4 cm oval and heterogeneous dense mass with partially obscured calcified margins, occupying the subareolar region with central macro calcification. There was no associated nipple retraction or architectural distortion.

Ultrasound (Fig 2) showed a 4.2 cm oval complex cystic mass with micro-lobulated margins, parallel to the skin. The cystic component showed posterior enhancement. The solid component showed central and peripheral vascularization with no posterior features. The lesion was categorized as Breast Imaging Reporting and Data System (BI-RADS) category 4.

A fine needle aspiration (FNA) was performed using ultrasound, in favor of a mucinous adenocarcinoma. Then an ultrasound-guided core biopsy was performed. Histopathologic examination (Fig 3) revealed the presence of carcinoma with squamous and chondroid inflections. Immuno-histochemistry study demonstrated a triple negative tumour with a low proliferative index. Pathological result suggested the diagnosis of a tumor of the salivary gland. The definitive diagnosis was established on the excision specimen, which revealed a pleomorphic adenoma developed into an intraductal papilloma of uncertain malignant potential.

Pleomorphic adenoma (PA) is the most common benign tumour of the salivary glands, specifically the parotid gland; however, it is among the least common tumour of the mammary gland [1]. It has also been described in other rare anatomic locations [2].

PA of the breast was first described by Lecène in 1906 [3], it is characterized by a mixture of epithelial/myoepithelial and myxomatous/cartilaginous elements [4].
Given the similarities in embryogenesis of the breast and salivary glands, this type of tumour can affect both locations [1,5,6].

It affects women ranging between 23 to 78 years [4]. Only six cases have been reported in the male breast [7].

Clinically, it can be asymptomatic or present as a slowly enlarging mass, usually periareolar in location [1], with one case reported arising away from the nipple [5]. Most of published cases of PA are around 2 cm in size [1,8] with one reported case growing up to 20 cm in size [5].

PA has variable and non-specific imaging appearances. On mammography, it is typically visualized as a well-defined hyper dense solitary mass; however, it may also exhibit ill-defined borders with numerous coarse, or diffuse irregular central calcifications, densely and partly calcified appearance and rarely multiple nodules [1,4,5,9].

Case reports describe two ultrasonographic aspects of PA of the mammary gland. First one is fibroadenoma-like appearance [4,5]. The second one is complex cystic mass with central vascularization within the solid component [10,11].

On magnetic resonance imaging (MRI), pleomorphic adenoma of the salivary gland and the breast share similar features including a well-defined border and hyper-intensity on T2-weighted imaging due to their rich myxoid matrix [11].

Diagnosing PA based solely on imaging features is challenging due to non-pathognomonic appearances. The diagnosis is made histologically by excision but nowadays tissue sampling by core biopsy is accepted [4].

A cellular component consisting of epithelial and myoepithelial cells within a chondromyxoid stromal component [1] characterize microscopic features of PA. Occasionally, malignant changes referred to as carcinoma ex PA can occur. However, this phenomenon was only reported in three cases to date [1].

Due to its high local recurrence rate and malignant potential, a clear resection margin and long-term observation are recommended [4].

Usually, the treatment consists of a lumpectomy, but in our case, due to the large size of the lesion, the number of satellite nodules and the uncertain malignant potential of the lesion, mastectomy was proposed.

Our case of PA of the breast is added to the small series of cases that were reported in the literature. It is important for clinicians to be aware of this rare condition and understand its diverse imaging appearances to avoid misdiagnosis and inappropriate treatment.

All patient data have been completely anonymised throughout the entire manuscript and related files.