What to Know About Mucinous (Colloid) Breast Cancer

Medically Reviewed by Sabrina Felson, MD on February 23, 2024
4 min read

Mucinous breast cancer is a rare type of cancer that makes up less than 2% of all breast cancer cases. It is an invasive ductal breast cancer.  

Mucinous or colloid breast cancer works in a similar way to other invasive ductal breast cancers. It begins in the milk duct of the breast and then spreads to the other tissues.

Fortunately, mucinous tumor cells are less aggressive than other kinds of invasive ductal cancer, and these cells respond well to treatment. Mucinous breast cancer has a better outcome than other typical types of invasive ductal cancers.

Also called colloid carcinoma, mucinous carcinoma is an uncommon type of breast cancer. It develops in the milk duct and spreads to other tissues. 

The tumor comprises abnormal cells, and in this type of breast cancer, these cells float in mucin, which is a primary component of a slimy substance called mucus.

The mucus is usually present in the lining of our body's inner surface. This mainly includes our digestive tract, lungs, liver, and other vital organs. Mucus is also produced by many cancer cells, including breast cancer cells.

One of the primary breast cancer causes is the mucus starting to surround the cancerous cells as a part of the tumor. If you look at it under a microscope, you will see the cancer cells spread throughout the mucus pools.

According to research, only 2% to 3% of invasive breast cancers are pure mucinous cancers. That means that mucinous carcinoma is the only cancer that is present within the tumor. 

On the other hand, about 5% of invasive breast cancers indicate the presence of mucinous elements within them.

Mucinous carcinoma mainly affects women and is very rare in men. 

Mucinous breast cancer can be diagnosed at any stage of a female's life. Primarily, it affects women after they reach menopause. The average age at which patients are diagnosed is in their 60s or early 70s.

Breast cancers usually show no symptoms at first. Mucinous carcinoma also doesn't have any signs in the beginning, but over time, you may start to see a lump growing in your breast that grows large enough to be seen.

You can even feel this lump during self-examination or at a doctor's appointment. The average size of mucinous carcinoma is about 3 centimeters (cm), but some people may have a bit smaller or larger lump.

The doctor follows many steps to diagnose mucinous carcinoma, including:

A Physical Examination

The doctor physically examines your breast to identify a lump. You can also feel it during a self-exam.

A Mammogram 

The doctor then looks for evidence of cancer in other parts of the breast. They will do a screening mammogram test to detect the location of the tumor. The mucinous carcinoma usually looks like a non-cancerous breast lump.

A mucinous carcinoma has well-defined edges that press the nearby breast tissue, but it doesn't grow or invade these tissues. This type of tumor also doesn't have calcifications, which are calcium deposits that appear as white specks.


This gives the doctor clear images of breast tissues.

Magnetic Resonance Imaging (MRI) 

The MRI gives clearer images of the breast to check other areas affected by cancer.


In this process, the doctor makes a small incision to take out the tumor. They may also use a needle to obtain tissue samples from the doubtful areas and examine them under a microscope.

The mucinous breast cancer treatment plan includes surgery to remove cancer from the breast and any affected lymph nodes. 

Common surgical procedures are:


As part of this method, the surgeon removes the tumor-containing part of your breast along with some surrounding normal tissue. They may also go for a sentinel node biopsy, which involves the removal of 1 or 2 nodes.

If the tumor is diagnosed as pure mucinous, your surgeon may not go for a sentinel node biopsy. That's because the risk for the tumor to spread in the lymph nodes is not high in such cases.

Simple Mastectomy

This process only involves the removal of the breast and not the lymph nodes. The surgeon may perform a sentinel node biopsy to confirm the spread of the tumor to the nearby lymph nodes.


This is the standard treatment for all types of cancer. It involves the insertion of anti-cancer medications in the vein or taking a pill. Both ways, the medicine needs to travel through the bloodstream and reach all parts of the body. 

Chemotherapy is used to destroy all the cancer cells that may be present in the body from the original tumor.

The doctor develops your treatment plan based on the features of the tumor (cell type, tumor grade, and hormone receptor status) and the cancer stage (tumor size and node status). 

Some Additional Therapies

  • The lumpectomy is usually followed by radiation therapy. In this process, high-intensity rays are used to damage the remaining cancerous cells, but doctors don't fully support the option of radiation therapy in pure mucinous carcinoma treatment.
  • In hormonal therapy, the doctor prescribes certain medications, such as an aromatase inhibitor or Soltamox (tamoxifen). These medicines work effectively to block or lower the effects of estrogen in the body. Since mucinous carcinoma is estrogen or progesterone-receptor positive, this therapy works efficiently.