Mucinous (Colloid) Carcinoma of the Breast

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Mucinous (colloid) carcinoma is a rare type of invasive breast cancer that is formed when cancer cells within your breast produce mucous. This mucous contains breast cancer cells that are easily distinguished from normal cells under a microscope. Together, the mucous and cancer cells form a jelly-like tumor. Most mucinous carcinomas of the breast are estrogen-receptor positive and HER2/neu negative. This type of breast cancer rarely spreads to your lymph nodes. It's also known as colloid carcinoma, or a mucous tumor.

An Uncommon Diagnosis

Mucinous carcinoma of the breast is a rare type of invasive breast cancer, diagnosed in less than 3 percent of all women diagnosed with breast cancer. It is not a mucinous disorder called "mucocele-like tumor (MLT)," which is often associated with atypical ductal hyperplasia (ADH) or ductal carcinoma in situ (DCIS). Making a distinction between a diagnosis of a mucinous carcinoma and a mucocele-like tumor is difficult and usually requires a biopsy and careful pathological examination.


A gelatinous tumor of mucinous carcinoma of the breast will feel like a slightly bumpy water balloon, similar to harmless fluid-filled cysts. Smaller tumors may be too little to detect with your fingers, but larger tumors may press on surrounding breast tissue and cause it to feel tender. During your regular breast self-exam, if you feel an area that won't compress like the rest of your breast tissue, get it checked out by a health professional.


  • Mammogram – A mucinous carcinoma of the breast will often appear on a mammogram as a mass with distinct borders, having a bumpy shape. These can sometimes look like benign masses on a mammogram.
  • Breast ultrasound – A little less than half of all mucinous carcinomas will be seen on a breast ultrasound, and the smaller tumors tend to hide within fatty tissue.
  • Open surgical biopsy – A tissue sample is taken and tested for specific characteristics in the lab.


Mucinous carcinoma of the breast usually appears in older women (ages 48 to 82) and is a medium- to- low-grade slow-growing type of breast cancer. Since it is not aggressive, your outlook, or prognosis if you are diagnosed with this type of breast cancer, is better than most other invasive breast cancers. A study done in western Australia found that, in most cases of mucinous carcinoma, the cancer did not spread to the lymph nodes nor metastasize to other parts of the body.


Mucinous carcinoma should be treated to get rid of the cancer and to prevent it from returning (recurrence). Treatments may include:

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Article Sources
  • Clinical Radiology. Volume 61, Issue 5, May 2006, Pages 423-430. Screen-detected mucinous breast carcinoma: Potential for delayed diagnosis. R. Dhillon, P. Depreea, C. Metcalfb and E. Wyliea.