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Sidney Kimmel Cancer Center / Centers & Clinics

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Metaplastic Breast Cancer

Metaplastic Breast Cancer Diagnosis

Metaplastic breast cancer is a rare form of breast cancer, accounting for fewer than 1% of all breast cancers.  It differs from the more common kinds of breast cancer in both its makeup and in the way it behaves. 

Like invasive ductal cancer, metaplastic breast cancer begins in the milk duct of the breast before spreading to the tissue around the duct.  What makes a metaplastic tumor different is the kinds of cells that make up the tumor.

When the cells of an invasive ductal tumor are examined under a microscope, they appear abnormal, but still look like ductal cells.  Metaplastic tumors may contain some of these breast cells, too, but they also contain cells that look like the soft tissue and connective tissue in the breast.  It is thought that the ductal cells have undergone a change in form (metaplasia) to become completely different cells, though it is not known exactly how or why this occurs.

Metaplastic breast cancers can also behave more aggressively than other kinds of breast cancers. 

  • Metaplastic tumors are often, though not always, “triple-negative”, which means that they test negative for estrogen and progesterone receptors, as well as for the HER2/neu protein. 
  • Metaplastic tumor cells are often found to be high grade, which means that they look very different from normal cells and are dividing rapidly.  
  • Metaplastic tumors are, on average, larger at diagnosis. 
  • More often than in other kinds of breast cancer, women with metaplastic breast cancer can have metastasis (when the cancer has spread beyond the breast) and may be more likely to recur (come back later in another part of the body).

Metaplastic Breast Cancer Staging and Treatment

Treatment  of metaplastic breast cancer is similar to that of more common types of breast cancer, and you can expect to receive some combination of both local therapy and systemic therapy. 

Local therapy is aimed at preventing the cancer from coming back in the breast. Local therapy includes surgery (lumpectomy or mastectomy), and may include radiation. 

Systemic therapy is used to prevent the disease from coming back or spreading to another part of the body.  This may include endocrine (hormone) therapy, chemotherapy, and therapy that targets the HER2 protein.  Sometimes different types of treatment are used together to achieve the best result.

Your treatment plan will be based on the features of the tumor (type of cells, tumor grade, hormone receptor status, and HER2 status) and the stage of the disease (tumor size and node status). Your oncology team will recommend a treatment plan based on what is known about metaplastic breast cancer in general and tailored specifically to your disease.