Mucinous carcinoma (sometimes referred to as glioid carcinoma) is a rare subtype of invasive ductal carcinoma (tumors that originate in the ducts but grow outside of them), accounting for approximately 2-3% of all breast cancers. Mucinous carcinoma microscopically consists of heterogeneous cells floating in pools of mucus, and this sticky, smooth mucus is an important component of mucinous carcinoma. Normally, mucus is mostly found in the digestive tract, lungs, liver and some other important organs in the body. Many types of tumor cells, including most breast cancer cells, also produce some mucus. In mucinous carcinoma, however, the mucus is the main component of the tumor and they are distributed around the breast tumor cells. Mucinous carcinoma is commonly seen in postmenopausal women. Some studies have found that the age at diagnosis of mucinous carcinoma is usually ≥ 60 years. Breast physical exam: Your doctor may find a mass during a physical exam, or you may palpate a mass during a breast self-exam. Mammogram, ultrasound, MRI: To find out about the mass and to see if there are any other tumor manifestations in other parts of the bilateral breast. A screening mammogram may detect a mucinous carcinoma, but it often appears to be a benign breast mass. Mucinous carcinoma is well-defined and pushes against the surrounding normal breast tissue, but does not infiltrate and grow into it. Biopsy: Removal of some or all of the tumor tissue for microscopic examination. A special sampling needle can be used to remove part of the tumor specimen, or the mass can be removed through a small breast incision for examination. Biopsy is a key part of confirming the diagnosis, as imaging alone does not distinguish mucinous carcinoma from other types of breast cancer or even benign (non-cancerous) breast disease. Treatment may include the following: Surgery to remove the tumor and metastatic lymph nodes. The possible procedures are: Breast conserving surgery: removal of the mass and some of the surrounding normal breast tissue. An anterior lymph node biopsy may also be performed to remove some of the lymph nodes for examination. Total breast/simple mastectomy: The entire breast tissue is removed. Possible anterior sentinel lymph node examination. Modified radical mastectomy: Removal of the breast and the chest wall muscles beneath it, as well as some axillary lymph nodes. Mucinous carcinoma alone often does not spread beyond the primary site, so this procedure is less commonly used. Adjuvant therapy, such as endocrine therapy and/or chemotherapy Endocrine therapy: taking drugs such as tamoxifen or AI, which either block the effects of estrogen or can lower the level of estrogen in the body. Almost all mucinous cancers are estrogen receptor positive, so endocrine therapy drugs will work. Adjuvant endocrine therapy can reduce the chance of breast cancer recurrence. Chemotherapy is given in the form of oral chemotherapy pills or intravenous chemotherapy drips. The drugs travel through the bloodstream to all parts of the body. The main purpose of chemotherapy is to destroy tumor cells that may have spread from the primary site to other parts of the body. The significance of chemotherapy for mucinous carcinoma alone is still a matter of debate.