Mucinous breast cancer

Mucinous breast cancer is known by this name because when it’s looked at under a microscope, the cells are surrounded by mucus.

Mucinous breast cancer accounts for fewer than 2% of all breast cancers. It’s often found alongside another type of breast cancer called invasive ductal breast cancer (also called ‘no special type’ or NST) and may then be referred to as ‘mixed’.

Mucinous breast cancer generally has a better prognosis (outlook) than most other types of invasive breast cancer.


Mucinous breast cancer is diagnosed in the same way as other breast cancers by using a range of tests. These include a mammogram (breast x-ray) and/or an ultrasound scan followed by a core biopsy or fine needle aspiration (FNA).

Find out more about diagnosing breast cancer.


As with all types of breast cancer, the features of your mucinous breast cancer will affect what treatments you might be offered.


Surgery is usually the first treatment for mucinous breast cancer.

This may be:

  • breast-conserving surgery, usually called a wide local excision or lumpectomy, which is the removal of the cancer with a margin (border) of normal breast tissue around it
  • mastectomy, which is the removal of all the breast tissue including the nipple area.

Sometimes after breast conserving surgery more surgery is needed if the margin of normal tissue (surrounding the cancer) removed during the first operation is not clear. This is to ensure that all the cancer has been removed. In some cases this second operation will be a mastectomy.

Your specialist team will also want to check whether breast cancer cells have spread from the breast to the lymph nodes (glands) under the arm (the axilla). This helps them decide whether you will benefit from additional treatment after surgery. To do this, your surgeon is likely to recommend an operation to remove either some of the lymph nodes (a lymph node sample or biopsy) or all of them (a lymph node clearance/ axillary clearance).

Sentinel lymph node biopsy is widely used for people with breast cancer whose tests before surgery show no evidence of the lymph nodes containing cancer cells. It identifies whether the first lymph node (or nodes) is clear of cancer cells. If it is, this usually means the other nodes are clear too, so no more will need to be removed.

However, your surgeon will discuss whether or not this is an option for you.

Find out more information about breast surgery, including lymph node removal and sentinel lymph node biopsy.

Adjuvant (additional) treatment

After surgery, you may need other treatments. This is called adjuvant therapy and can include:

  • chemotherapy
  • radiotherapy
  • hormone therapy
  • targeted therapy.

The aim of these treatments is to reduce the risk of breast cancer coming back in the same breast or developing in the other breast, or spreading somewhere else in the body.

Sometimes chemotherapy or hormone therapy may be given before surgery. This is known as neo-adjuvant or primary therapy.


Depending on various features of the cancer, chemotherapy may be recommended for some people. Because it’s less common for mucinous breast cancer to have spread to the lymph nodes under the arm, and it’s more likely to grow more slowly than other types of breast cancer, chemotherapy is not often used.


If you have breast-conserving surgery you will usually be offered radiotherapy to the breast to reduce the risk of the cancer coming back in the same breast. Sometimes you may be offered radiotherapy to the nodes under your arm.

In some circumstances, you may be recommended to have radiotherapy to the chest wall after a mastectomy, for example if some of the lymph nodes under the arm are affected.

Hormone (endocrine) therapy

All breast cancers are tested for oestrogen receptors using tissue from a biopsy or after surgery. Most mucinous breast cancers are oestrogen receptor positive. Hormone therapy will only be prescribed if your breast cancer has receptors within the cell that bind to the female hormone oestrogen and stimulate the cancer to grow (known as oestrogen receptor positive or ER+ breast cancer).

Find out more about when hormone therapy is given.

Targeted therapies (sometimes called biological therapies)

This is a group of drugs that block the growth and spread of cancer. They target and interfere with processes in the cells that cause cancer to grow.

The most widely-used targeted therapy is trastuzumab (Herceptin). Only people whose cancer has high levels of HER2 (referred to as being HER2 positive or HER2+), a protein that makes cancer cells grow, will benefit from having trastuzumab.

Mucinous breast cancer tends to be HER2 negative. If your cancer is found to be HER2 negative, then trastuzumab will not be of benefit to you.

Last reviewed: February 2016
Next planned review begins 2018

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