Teaching Case

A 29-year-old woman with no significant medical history presented with a rapidly growing and painful left breast mass.
On examination, the breast mass was large, measuring approximately 8 cm and was tender to palpation. There was no palpable axillary or supraclavicular lymphadenopathy.

On mammography a large, round, high density mass was seen occupying the upper outer quadrant of the left breast, mostly circumscribed with partially ill defined margins and without microcalcifications (Fig. 1). On ultrasound the lesion was complex cystic with circumscribed, partially microlobulated margins (Fig.2).The solid component of the lesion were vascularised on colour-doppler ultrasound (Fig.3).
Breast MR was performed and revealed a round, lobulated mass with central hyperintense component related to necrosis and a peripheral isointense irregular solid component on T2-WI (Fig.4).The lesion showed rapid and heterogeneous contrast enhancement of the solid component (Fig.5). No other lesions were seen.
Core biopsy was performed and the result was metaplastic breast carcinoma.
The patient underwent left radical mastectomy and axillary lymph node dissection. Histology confirmed the diagnosis of metaplastic breast carcinoma with squamous cell carcinoma differentiation, negative for estrogen and progesterone receptors and HER-2 negative. No axillary lymph node involvement was found. The patient received adjuvant chemotherapy.

Metaplastic carcinoma of the breast is a rare type of breast cancer, accounting for 0.02% of all breast cancers [1]. Metaplastic breast carcinomas are a heterogeneous group of neoplasms with mixed epithelial, usually ductal carcinoma, and mesenchymal differentiation. Five principal variants were suggested, including matrix-producing carcinoma, spindle-cell carcinoma, squamous cell carcinoma, carcinosarcoma, and metaplastic carcinoma with osteoclastic giant cells [2]. The mesenchymal element involved in the case described was squamous cell carcinoma.

Metaplastic breast carcinomas tend to be present at an advanced stage, frequently as a large and painful palpable mass.

Metaplastic tumours usually are "triple negative" with estrogen and progesterone receptors and Her-2 negative [1], as in the case presented. These tumours tend to have a low incidence of regional lymph node involvement and have a great tendency for early hematogenous dissemination and local recurrence.

As metaplastic carcinomas [3] have a significantly worse overall survival rate, it is important to differentiate them from other breast carcinomas for treatment planning and prognosis. However metaplastic carcinomas can display benign imaging features, and may be misinterpretated as a benign or a probably benign lesion, delaying the diagnosis.

There are no specific or distinctive imaging findings of metaplastic carcinomas, but the most common mammographic appearance described in the literature are a high-density round or oval mass which is predominantly circumscribed or microlobulated, usually without prominent spiculations and usually without associated microcalcifications. On ultrasound, metaplastic carcinomas can be seen as a round or oval lobulated masses with solid and cystic components and with circumscribed or microlobulated contours and less frequently with posterior acoustic enhancement [4]. On MR imaging, the lesions are usually isointense or hypointense on T1-WI, as in other types of invasive carcinomas. However on T2-WI metaplastic tumuors are generally hyperintense due to the necrotic component, which can also be observed in carcinomas with mucoid content and in infiltrating ductal carcinoma with an abundant necrotic component, so this hyperintensity on T2-WI is useful in differentiating these tumours from other histologic types of invasive carcinoma [5]. Most of these common imaging features were seen in the case presented.

The diagnosis of metaplastic breast carcinoma can be made with aspiration cytology or core biopsy, but inadequate samples especially in cases of abundant necrosis or hemorrhage may provide diagnostic errors and excisional biopsy may be needed in these cases.

Most metaplastic breast carcinomas are treated by mastectomy, with or without axillary node dissection and in the majority of cases with adjuvant chemotherapy.