Mucinous carcinoma is a rare type of cancer that primarily develops in the breast. This form of breast cancer tends to be less aggressive, and the outlook is often good.

Mucinous carcinoma accounts for 1–7% of all breast cancer cases. It usually develops in women over 60, and it is extremely rare in men.

Mucinous carcinoma is an invasive cancer, meaning that it can spread to other parts of the body. However, it is less aggressive than other invasive types of cancer, and it generally responds well to treatment.

Less commonly, mucinous carcinoma first develops in areas other than the breast, such as the colon or rectum.

In this article, we discuss the symptoms, causes, and survival rates associated with mucinous carcinoma. We also explore treatment options.

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Mucinous carcinoma is a type of cancer that can occur in the breast.

Mucinous carcinoma is a type of invasive cancer in which mucin — the main component of mucus — surrounds the cancer cells.

While this form of cancer can develop in any part of the body that produces mucin, most cases occur in the breast. Colloid carcinoma is another name for mucinous carcinoma of the breast.

This type of cancer can form alongside other cancer cells, such as those of ductal breast cancer. When this happens, doctors refer to it as "mixed mucinous carcinoma." By contrast, "pure" mucinous carcinoma has 90–100% mucinous cells.

According to some estimates, 2–3% of invasive breast cancer cases are pure mucinous carcinomas, while 5% are mixed mucinous carcinomas.

Mucinous carcinoma can also develop in the lungs or in the colon or rectum, in which case the diagnosis may be colorectal cancer.

Initially, mucinous carcinoma of the breast may not cause symptoms.

As the cancer develops, a lump may form in the breast tissue, and a person may eventually be able to feel it during an examination.

On average, a mucinous carcinoma lump measures 3 centimeters.

Breast cancer symptoms besides a lump can include:

  • armpit pain
  • breast pain
  • changes to breast size or shape
  • nipple changes
  • nipple discharge
  • puckering or dimpling of the skin on the breast
  • swelling under the arm

Colorectal cancer symptoms can include:

The symptoms of mucinous carcinoma of the lung are the same as symptoms of other types of lung cancer. They can include:

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Drinking alcohol can increase a person's risk of developing breast cancer.

Cancer occurs when the body's regular cellular process breaks down: Old and damaged cells do not die when they should, and new cells grow when they should not.

For mucinous carcinoma of the breast, causes and risk factors are similar to those of breast cancers in general. It is likely that a combination of genetics and environmental factors lead to the cancer developing.

Risk factors for breast cancer include:

  • Genetics. Breast cancer can occur due to inherited mutations, such as those involving the BRCA1 and BRCA2 genes. Having these genetic mutations or a family history of cancer increases a person's risk.
  • Personal medical history. People with a history of breast cancer are more likely to develop mucinous carcinoma or other types of cancer.
  • Age. The risk of breast cancer increases with age. Mucinous carcinoma is most common in women over 60.
  • Obesity. Obesity increases the risk of breast cancer.
  • Alcohol use. People who drink alcohol are more likely to develop breast cancer than those who do not.
  • Radiation treatment. Exposure to radiation around the chest can increase breast cancer risk.

Also, the following can each increase breast cancer risk:

  • having menstrual cycles from an early age
  • going through menopause at an older age
  • giving birth for the first time at an older age
  • never giving birth

In addition, breast cancer risk increases while hormone therapy is ongoing.

Risk factors for colon cancer include:

  • a lack of physical activity
  • a diet that is low in fiber and high in fat
  • tobacco use
  • heavy alcohol use
  • diabetes
  • obesity
  • a family history of colon cancer
  • a personal history of colorectal cancer or inflammatory bowel disorder
  • race, with African American people having a higher risk
  • age, with older adults having a higher risk

The risk factors for mucinous carcinoma of the lung are the same as those for other types of lung cancer. They include:

  • tobacco use
  • exposure to secondhand smoke
  • exposure to chemicals that cause cancer, such as asbestos, arsenic, and radon
  • a family history of lung cancer

Treatment for mucinous carcinoma depends on the stage of the cancer, the person's health status, and the affected area of the body.

Also, pure mucinous carcinoma may require less aggressive treatment than the mixed form.

Treatment options include the following:

Surgery

The aim of surgery is to remove the cancerous cells and any affected lymph nodes.

When treating mucinous carcinoma of the breast, the surgeon may remove the portion of the breast that contains the lump, in a procedure called a lumpectomy. Or, they may remove the entire breast, in a mastectomy.

Chemotherapy

Chemotherapy involves taking medications to destroy cancer cells that may be present outside the main lump.

Hormone therapy

Hormone therapy is generally an effective treatment for mucinous carcinoma of the breast. It can also lower the risk of the cancer returning.

Hormone therapy aims to reduce the amount of estrogen in the body or block its effects. This type of treatment is effective for hormone-positive breast cancers.

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Survival rates for people with mucinous carcinoma are high.

People with pure mucinous carcinoma of the breast tend to have higher survival rates than those with other types of malignant breast cancer. A 2015 review, for example, reports that there is a 90% survival rate at 10 years after diagnosis.

The survival rates for people with either mixed mucinous carcinoma or mucinous carcinoma in the lungs or colon are not as high.

However, it is important to remember that survival rates give only a general picture. Each person's outlook is different.

The outlook depends upon specific factors, such as the stage of cancer at diagnosis, the size of the tumor, and the person's general health. A person should discuss their outlook with their doctor, who can take all of the relevant factors into account.

Mucinous carcinoma is an uncommon type of cancer.

When it first develops in the breast, a person tends to have a better outlook than people with other forms of invasive breast cancer.

For the best prognosis, it is important for a doctor to detect and treat the cancer at an early stage. Regular breast self-exams and mammograms are important.

It is also helpful to reduce cancer risk factors whenever possible, such as by avoiding tobacco smoke, eating a healthful diet, and exercising regularly.

When mucinous carcinoma first develops somewhere other than the breast, the survival rates are less high. Early diagnosis and treatment lead to the best outlook.