Symptoms and Diagnosis of Mucinous Carcinoma of the Breast

In this section you can learn about symptoms of mucinous carcinoma and different diagnosing methods.

Signs and symptoms

Like other types of breast cancer, mucinous carcinoma of the breast may not cause any symptoms at first. Over time, a lump may grow large enough to be felt during breast self-exam or examination by a doctor. The tumors tend to range in size from 1 cm to 5 cm.


Diagnosing mucinous carcinoma usually involves a combination of steps:

  • A physical examination of the breasts. Your doctor may be able to feel the lump in the breast, or you may feel it yourself during a breast self-exam.
  • A mammogram to locate the tumor and check for evidence of cancer in other areas of the breast. A screening mammogram may be able to detect a mucinous carcinoma, but it often looks like a benign (non-cancerous) breast lump. A mucinous carcinoma has well-defined edges and pushes against nearby healthy breast tissue, but does not invade it (grow into it).
  • Ultrasound uses sound waves to obtain images of breast tissue.
  • MRI to obtain additional images of the breast and check for other areas of cancer.
  • Biopsy involves making a small incision and taking out all of the tumor, or using a special needle to remove tissue samples from the suspicious area, for examination under a microscope. Biopsy is the key to accurate diagnosis, because imaging tests alone can’t tell the difference between mucinous carcinoma, other types of breast cancer, and benign breast lumps.

When a pathologist examines the tissue under a microscope, he or she looks for small clusters of tumor cells that appear to “float” in pools of mucin. The tumor may be made up mostly of mucin, or it may be made up mostly of cancer cells separated by small amounts of mucin.

Mucinous carcinoma also can be found near, or mixed in with, other more common types of breast cancer. Sometimes a ductal carcinoma in situ (or DCIS, cancer that has not spread outside the milk duct) is found near the mucinous carcinoma. A mucinous carcinoma also may have some areas within it that contain invasive ductal carcinoma cells. If the invasive ductal carcinoma cells make up more than 10% of the tumor, the cancer would be called a “mixed” mucinous carcinoma. A “pure” mucinous carcinoma means that at least 90% of the cells are mucinous.

As with the other rare subtypes of breast cancer, diagnosing mucinous carcinoma takes special skill. You may want to seek a second opinion from another hospital pathology lab if this is your diagnosis.

There are some other key features of pure mucinous carcinoma:

  • Hormone-receptor-positive: Studies show that pure mucinous carcinoma tests positive for estrogen receptors 90-100% of the time and for progesterone receptors in 50-68% of cases.
  • HER2-negative: Mucinous carcinoma usually tests negative for receptors for the protein HER2/neu.
  • Negative lymph nodes: Pure mucinous carcinoma rarely spreads to the lymph nodes, especially if the tumor is 1-2 cm or smaller. Larger tumors may involve spread to the lymph nodes. Sometimes, cancer in the lymph nodes indicates that the tumor is actually a mixed mucinous carcinoma, with invasive ductal carcinoma cells present.