What is a Metaplastic Carcinoma?

The term metaplastic carcinoma refers to a group of invasive carcinomas that appear different from all other types of invasive carcinoma because they have a unique appearance under the microscope, including having bone or cartilage or sometimes not looking at all like a typical invasive carcinoma.

There are several types of metaplastic carcinoma including spindle cell carcinoma, squamous cell carcinoma, and matrix-producing carcinoma.  Many times the cancer is composed of usual invasive carcinoma NST mixed with the metaplastic areas and thus it is easy for the pathologist to determine this is a metaplastic carcinoma.  When there is no usual type invasive carcinoma, sometimes special studies such as immunohistochemistry are needed to help the pathologist make this diagnosis.

  • Spindle cell carcinoma:  This refers to a type of metaplastic breast cancer in which the cells no longer look like breast epithelium and have a spindled appearance more like a sarcoma, which is a cancer of the body’s supporting structures. Sometimes the pathologist can see a typical invasive breast cancer mixed in with the spindle cell areas and can make the diagnosis of metaplastic carcinoma without additional special studies.  However, it may be necessary for the pathologist to use immunohistochemistry to show that the cancer is a carcinoma, meaning the cells are epithelial.
  • Squamous cell carcinoma:  This is a type of metaplastic carcinoma which is similar in appearance to squamous cell carcinomas outside of the breast, such as on the skin surface.  Often, these cancers are mixed with a spindle cell carcinoma and are called “spindled and squamous cell carcinoma” (see above).
  • Matrix-producing carcinoma: These cancers generally are composed of areas of usual type invasive carcinoma and areas where the cancer has cartilage or bone production. Depending on the amount of the metaplastic component, sometimes it is difficult for the pathologist to determine if this is a carcinoma or a sarcoma. Adequate sampling of the tumor and immunohistochemistry can help.
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