What You Should Know About Metaplastic Breast Cancer

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What do we know about metaplastic breast cancer?. Annette Bunch/Moment/Getty Images

Metaplastic breast cancer (metaplastic carcinoma of the breast) is a very uncommon type of breast cancer. It can be somewhat tricky to treat and relatively little is known about the causes or the long-term prognosis. These tumors tend to be aggressive, and are less likely to be estrogen-receptor positive or HER2 positive, which limits treatment options. They also tend to respond poorly to chemotherapy. Radiation therapy, however, can be effective, and newer targeted therapies, such as mTOR inhibition may not only improve survival, but raise hope of better treatments in the near future.

Metaplastic breast cancer is a form of invasive ductal cancer, meaning that it forms in the milk ducts and then moves into other tissues of the breast. These cancers differ from other types of breast cancer in that these tumors often contain other types of tissue which are not normally found in the breast. For example, these tumors may include squamous cells (skin) or osseous cells (bone cells).

Metaplastic vs. Metastatic

The term metaplastic sounds very much like metastatic, but the two have very different meanings. Metaplastic comes from the Greek phrase for "changed in form,'' which is why it is used to describe cells that appear to have changed into those of another part of the body. Metastatic comes from the Greek phrase for "changed in place,'' describing cancer that has spread from its original site to other areas.

Metaplastic breast cancer may also be confused for the term metaplasia, as it is sometimes used to describe abnormal findings on a biopsy. When the term metaplasia is used in a pathology report describing abnormal cells in another type of tissue, it is often used to describe cells that are abnormal but not yet cancerous. 


Some women with metaplastic breast cancer have no symptoms at all and are identified through routine screening. For others, the symptoms are essentially the same as for other types of breast cancer. These may include:

  • Lumps or thickening in the breast that were not there before
  • Tenderness, discharge or change in appearance of the nipple
  • Changes in the appearance of breast skin: redness, scaling, puckering or dimpling
  • Irritation of the breast, including redness, swelling, and rash
  • Unexplained pain in the breast, especially with any of the above symptoms


Tests to diagnose breast cancer are similar no matter what type of cancer is present. Imaging tests that may be used include:

  • Diagnostic mammography. This is much like your routine screening mammogram, except that diagnosing cancer (rather than just checking for cancer) requires more images to be taken and examined.
  • Ultrasound. This uses high-frequency sound waves to produce images of breast tissue. These images help doctors to determine whether a lump in the breast is a fluid-filled cyst or a solid tumor.
  • Magnetic resonance imaging (MRI). This uses magnetic fields to produce images of the inside of the body.
  • Computed tomography (CT or CAT) scan. This creates multiple "slice by slice" pictures of the inside of the body, then combines them into a detailed cross-section picture that can show the presence of tumors.
  • Positron-emission tomography (PET) scan. After an injection of radioactive sugar molecules, a PET scan is taken to see which areas of the body are absorbing the sugar most quickly. Because cancer cells thrive on sugar, they "light up" on a PET scan.
  • PET-CT scan. This combines the technology of the PET and CT scans, allowing doctors to observe which cells may be cancerous and determine more precisely where they are in the body.

    On mammography, metaplastic breast cancer can appear very similar to both ductal carcinoma and benign masses which can make the diagnosis more challenging.

    Breast Biopsy

    Any of the imaging tests above may be helpful in learning more about a tumor, but a breast biopsy is needed to determine the exact type of breast cancer and to learn about characteristics of the tumor, such as tumor grade (the aggressiveness of the tumor) and receptor status.

    To specifically diagnose metaplastic breast cancer, the breast tissue must be biopsied, meaning that a bit of tissue is removed from the breast (surgically or with a special needle) and examined under a microscope. A biopsy would generally follow some sort of imaging to confirm there is a cancerous tumor present (as opposed to a benign tumor, or a fluid-filled cyst).


    It's important to note that no two breast cancers are alike, even tumors that are diagnosed as metaplastic breast cancer. Any of these characteristics may not be true for your particular cancer. Metaplastic breast tumors tend to be aggressive and grow rapidly. They also tend to be resistant to both chemotherapy and hormonal therapies.


    Due to being so uncommon, the best treatment modalities aren't really known, but it appears that surgery to remove the tumor and radiation therapy are of greatest benefit. The low frequency of this type of tumor also means that a tried-and-true course of action in note readily apparent. Still, as with all cancer, treatment is at first guided by:

    • The size and location of the tumor
    • Whether the cancer has spread (this includes regional spread to lymph nodes as well as distant spread to areas such as the bones, liver, lungs, and brain)
    • The person's overall health
    • Age at diagnosis

    With these questions in mind, the first step is usually surgery to remove the visible tumor. From there, the following results from the biopsy can help determine further action:

    • Testing for hormone receptivity. Tests to look for estrogen and progesterone receptor positivity determine whether the cancer cells will respond well to hormone therapy, such as tamoxifen, or aromatase inhibitors as adjuvant therapy. Tamoxifen works by inhibiting the estrogen receptors on precancerous and cancerous breast cells, as estrogen binds with these receptors to cause growth in estrogen receptor-positive tumors. Aromatase inhibitors work by blocking the conversion of male hormones (androgens) to estrogen, thus reducing a growth factor for some breast cancers.
    • Testing for HER-2 protein. The HER2 protein is overproduced in about one-fourth of all breast cancers. If this protein is found in a biopsied tumor, then treatment with Herceptin (trastuzumab) may be an option. FDA-approved in 1998, Herceptin binds to the HER-2 protein on cancer cells, so that growth factors in the body cannot bind and cause the tumor to grow. Since Herceptin was approved, there are additional medications available as well for HER2 positive tumors.

      Best treatment options (in addition to hormonal or targeted therapies if the tumor is estrogen receptor or HER2 positive include:

      • Surgery: A lumpectomy or mastectomy is the most definitive treatment. Since metaplastic breast cancers tend to be larger than other types of breast cancer at diagnosis, mastectomy may be needed instead of lumpectomy.
      • Chemotherapy: Many of these cancers are at a higher stage than the average for breast cancer at diagnosis and therefore chemotherapy is often recommended. That said, chemotherapy does not appear to be as effective for metaplastic breast cancer.
      • Radiation therapy: One of the larger studies to date, a 2017 study looking at treatment options did find that adjuvant radiation therapy was important in preventing local and regional recurrences in metaplastic breast cancer.

      Treatment options for metaplastic cancers that are estrogen receptor and HER2 negative (triple negative) are more limited (since chemotherapy is not particularly effective), but recent research offers promise. A 2018 study looked at the response of these tumors to mTOR inhibition (a type of targeted therapy) with the drugs Afinitor (everolimus) or Torisel (temsirolimus). It was found that people with metaplastic triple negative breast cancers had better outcomes than those who had non-metaplastic triple negative tumors. Not only is this hopeful from a treatment standpoint, but it better identifies a pathway that may be targeted to stop these cancers in the future.


      Having such a rare form of breast cancer may leave you feeling isolated and confused. Here are some ways to help ease your concerns:

      • Find a support group. Your hospital or cancer treatment center may host support groups for breast cancer patients, or, at least, be able to refer you to one. Even if you are the only one in the group with this specific diagnosis, you are likely to meet women who are going through the same treatments and have the same questions as you do.
      • Get online.To connect with others who have metaplastic breast cancer, you can join online communities where patients share their experiences. The American Cancer Society has a great list of online support groups to get you started.
      • Consider a clinical trial. Your doctor may know of clinical trials that aim to learn more about your condition. Signing up for these trials may be a good way to help you feel more connected to the process and have a hand in discovering new treatment options. To learn more about the pros and cons of clinical trials and how to find one, consult the National Institutes of Health clinical trial website.
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