FINAL DIAGNOSIS: METAPLASTIC CARCINOMA OF THE BREAST, MATRIX PRODUCING TYPE, (POOR NUCLEAR GRADE)
Metaplastic carcinomas of the breast are uncommon tumors which histologically show cellular components with differentiation other than glandular. Classically, these tumors are divided into two main categories: tumors with squamous metaplasia, and tumors with heterologous components. The tumors with heterologous components may demonstrate spindle cell areas, cartilage formation, and bone formation, as well as rhabdomyoid (1), melanocytic (2), adipose and angiosarcomatous metaplasia (3). Morphologic classification divides these tumors into five subtypes: Matrix-Producing Carcinoma (I), Spindle Cell Carcinoma (II), Carcinosarcoma (III), Squamous Cell Carcinoma of Ductal Origin (IV), and Metaplastic Carcinoma with Osteoclastic Giant cells (V) (4,5,6,7,8).
Metaplastic carcinomas of the matrix producing type, of which this case is an example, tend to have cartilage or osseous elements as the heterologous component. The diagnostic feature of these lesions is the direct transition from the glandular component to the heterologous component. There is no spindle cell component or osteoclastic component between these two components, although areas of spindled cells may be present in the areas of the lesion. The carcinomatous component is usually moderately to poorly differentiated and intraductal components may be identified. The matrix produced varies from atypical chondroid-like matrix to hyaline cartilage to osteoid to bone. The cartilaginous matrix is made up of sulfated acid mucopolysaccharides which stain metachromatically with alcian blue and aldehyde-fuschin. This staining is resistant to predigestion with hyaluronidase and diastase. Immunohistochemistry shows positivity for keratin, S-100, and epithelial membrane antigen in the carcinomatous component. Sometimes this component will stain for vimentin. The metaplastic cells tend to be strongly positive for vimentin and S-100. Keratin and epithelial membrane antigen immunostaining is variable in the metaplastic matrix. The metaplastic matrix has also been reported to stain for actin. The origin of the matrix producing cells is thought to be precursors of epithelial or myoepithelial cells, due to the ability of these cells to undergo mesenchymal differentiation. (4)
The rarity of metaplastic carcinomas and the low frequency of axillary metastases makes it difficult to study the morphologic features which would correspond with prognosis. Predictably, prognosis in metaplastic carcinomas worsens with increasing stage of the tumor. Studies have reported 5-year disease free survival rates ranging from 38% (9) up to 86% (10). Axillary lymph node metastases and distal metastases may take the form of either a single component of a heterologous tumor or a mixture of the components seen in the original tumor. Overall, metaplastic carcinomas with heterologous components appear to have a worse prognosis, most likely due to the fact that these lesions tend to be poorly differentiated tumors.
The patient in this case underwent resection of her tumor and is currently asymptomatic. The patient is being followed and further information concerning her clinical course will be provided when available.
Contributed by Christine Dorvault, M.D., Hector Tobon, M.D., and Antonio J. Amortegui, M.D.