Metaplastic breast carcinoma

Metaplastic breast carcinoma (MBC), also known as spindle cell carcinoma of the breast (SpCC), is a rare form of primary breast malignancy and accounts < 5% of breast carcinomas.

These are scarce lesions, rarely seen in general radiology practice. The lesions usually present as a mass in postmenopausal women. The mammogram shows a lesion that is dense and has both smooth, defined margins and spiculated edges. The ultrasound images show mixed echogenicity lesions taller or tall as broad.

Epidemiology

Patients are commonly older than 50 years, with an average age at diagnosis ~55 years. 

Clinical presentation

These lesions present as a palpable mass lesion (often rapidly growing ^1,3) in postmenopausal women. Axillary node involvement at the time of diagnosis is uncommon.

Pathology

These lesions are considered ductal carcinomas that undergo metaplasia to a glandular growth pattern. There are five variants:

• matrix producing carcinoma of the breast
• squamous cell carcinoma of the breast
• spindle cell carcinoma of the breast
• carcinosarcoma of the breast (the rarest primary breast malignancy)
• metaplastic carcinoma of the breast with osteoclastic giant cells

Histology

These lesions have pathological features of both carcinoma and sarcoma. There is a mixture of glandular epithelial elements and mesenchymal malignant elements. The spindle cell component in 98% of SpCC is immunoreactive for keratin.

Genetics

Phyllodes tumors and sarcomas are usually negative for p63 expression. In metaplastic carcinoma, the sensitivity for p63 is 86.7% and the sensitivity is 99.4%.

Radiographic features

Mammography

On a mammogram, these are usually large lesions, mean diameter at the time of diagnosis is 4.2 cm. The lesions are rounded densities on mammography with margins that are both well defined and smooth and spiculated. Calcification is very rare. 

Ultrasound

On ultrasound the lesions are round to ovoid, maybe microlobulated, with solid and cystic components related to hemorrhage or necrosis. Most lesions have well-defined margins ³.

Breast MRI

• T2: often displays very high signal ²

Treatment and prognosis

Local recurrence generally not ominous and is fatal in ~30% of cases.