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Treatment of Mucinous Carcinoma of the Breast

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You and your doctor will work together to develop your treatment plan for mucinous carcinoma of the breast. If you have a pure mucinous carcinoma — meaning that 90-100% of the tumor is made up of the characteristic cells floating in mucus, without other types of breast cancer cells mixed in — it typically will require less treatment than other types of invasive ductal carcinoma (IDC). If another type of IDC is found to make up 10% or more of the tumor, you have “mixed” mucinous carcinoma. Your treatment plan will address both the mucinous carcinoma and the other IDC type. You can visit our Treatment for IDC section for more information.

Pure mucinous carcinoma is less likely to spread to the axillary (underarm) lymph nodes than other types of IDC. Estimates on how often this happens vary, but on average it’s thought to occur in about 15% of women with mucinous carcinoma.

Some recent research has suggested that, in cases of mucinous carcinoma, a certain percentage of women will have more than one mucinous tumor in the breast. For example, a 2009 study at M.D. Anderson Cancer Center found that, in a sample of more than 260 women with mucinous carcinoma, about 38% had more than one area of cancer within the breast. Research is ongoing, but you may want to discuss this information with your doctor and see what he or she recommends.

Your treatment plan for pure mucinous carcinoma can include:

  • Surgery to remove the cancer and, in some cases, any affected lymph nodes. Possible procedures are:
    • Lumpectomy: The surgeon removes only the part of your breast containing the tumor (the “lump”) and some of the normal tissue that surrounds it. A sentinel node biopsy (removal of 1-2 nodes) may be performed to check the node or nodes closest to the tumor for any signs of cancer spread. If your tumor is 100% mucinous, however, your surgeon may not think it’s necessary to biopsy the underarm lymph nodes. In such cases, the risk of spread to the lymph nodes is thought to be small. Other surgeons may still recommend the biopsy, though.
    • Total or simple mastectomy: Removal of the breast without removal of the axillary (underarm) lymph nodes. A sentinel node biopsy may be performed to check the node or nodes closest to the tumor for any signs of cancer spread.
  • Adjuvant (additional) therapy, such as radiation therapy, hormonal therapy, and/or chemotherapy.
    • If you have lumpectomy, it’s typically followed by radiation therapy, which directs high-energy rays at the area to destroy any remaining cancer cells. Doctors don’t always agree on whether radiation therapy is necessary for 100% pure mucinous carcinoma. More research is needed to know for sure; in the meantime, you and your doctor can discuss the best option for your case.
    • Hormonal therapy involves taking medications such as tamoxifen or an aromatase inhibitor, which either block the effects of estrogen or lower the amount of estrogen in the body. Almost all mucinous carcinomas are estrogen- and/or progesterone-receptor positive, which means that hormonal therapy is likely to be an effective treatment. Adjuvant hormonal therapy is given to lower the chances of the breast cancer coming back. However, if testing shows that a mucinous breast cancer is estrogen- and progesterone-receptor negative, other treatments may be considered.
    • Chemotherapy involves taking anti-cancer medicines in the form of a pill or directly into a vein. The medicines travel through the bloodstream to all parts of the body. The main goal is to destroy any cancer cells that may have broken away from the original tumor.
    Many doctors base their recommendations about adjuvant therapy for mucinous carcinoma on the size of the tumor and whether or not there is evidence of cancer in the lymph nodes. Some general guidelines follow — but remember that individual doctors may have different opinions about whether additional treatment is needed for mucinous carcinoma. You and your doctor can discuss what’s best for your particular situation.
    • If the tumor is smaller than 1 cm, with no cancer or just a very small amount of cancer (a 2-millimeter area or less) in one lymph node: No hormonal therapy or chemotherapy is typically recommended after surgery.
    • If the tumor is between 1 and 2.9 cm in size, with no cancer or just a very small amount of cancer found in 1 lymph node: Hormonal therapy is often considered as a next treatment, since most mucinous cancers are estrogen- and/or progesterone-receptor positive.
    • If the tumor is 3 cm or larger, with no cancer or just a very small amount of cancer in 1 lymph node: Hormonal therapy is typically recommended after surgery.

If larger amounts of cancer — each more than a 2-mm area — have spread to 1 or more underarm lymph nodes, then your doctor may suggest treating you with chemotherapy in addition to hormonal therapy.

Your doctor also may recommend chemotherapy if the mucinous cancer tests negative for estrogen and progesterone receptors, since hormonal therapy cannot be used in these cases. If your hormone receptor tests come back negative, be sure to ask for a repeat test. It’s unusual for a mucinous tumor to be hormone-receptor negative.

You and your doctor can discuss all of the risks and benefits of additional treatment beyond surgery. This decision may come down to what you and your doctor feel is best for you.

Mucinous carcinomas usually test negative for HER2 receptors, so cannot be treated with anti-HER2 medicines such as Enhertu (chemical name: fam-trastuzumab-deruxtecan-nxki), Herceptin (chemical name: trastuzumab)., Kadcyla (chemical name: T-DM1 or ado-trastuzumab), Nerlynx (chemical name: neratinib), Perjeta (chemical name: pertuzumab), and Tykerb (chemical name: lapatinib).

Still, be sure to confirm with your doctor whether or not you are a candidate for anti-HER2 medicines.

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