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Symptoms and Diagnosis of Mucinous Carcinoma of the Breast

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In this section you can learn about symptoms of mucinous carcinoma and how it’s diagnosed.

Signs and symptoms of mucinous carcinoma

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 average mucinous carcinoma is about 3 centimeters (cm), although they can be smaller or larger.

Diagnosis of mucinous carcinoma

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 often can detect a mucinous carcinoma, but it typically looks like a benign (non-cancerous) breast lump. A mucinous carcinoma usually has well-defined edges and pushes against nearby healthy breast tissue, but does not invade it (grow into it). It generally does not have the irregular borders and calcifications (calcium deposits that show up as white specks) that are often associated with other types of invasive breast cancer.
  • 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 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 often can’t distinguish mucinous carcinoma from 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 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, a 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 90-100% of the cells are mucinous.

Now or after surgery, the tissue should be tested for some other important features of a pure mucinous breast carcinoma:

  • Hormone-receptor-positive (HR+) status: Studies show that pure mucinous carcinoma tests positive for estrogen receptors 86-92% of the time and for progesterone receptors in 63-68% of cases.
  • HER2-negative (HER2-) status: Mucinous carcinoma tests negative for receptors for the protein HER2/neu nearly 100% of the time.

Both of these features — along with mucinous carcinoma’s tendency to stay within the breast — are reasons you may hear your doctor say that mucinous carcinoma has a “favorable prognosis” or “good outlook.” HR+/HER2- cancers tend to be less aggressive cancers. Research also suggests that mucinous carcinomas are much less likely to have the chromosomal abnormalities typically found with invasive breast cancers. This means they are more like normal, healthy cells and less likely to grow and spread quickly.

As with the other less common types of breast cancer, diagnosing mucinous carcinoma takes special skill. You may want to ask for a second opinion if this is your diagnosis. You also can ask for repeat testing if you are told you have a tubular carcinoma that’s hormone-receptor-negative or HER2-positive.

For more information about the process of diagnosing the cancer, see Your Diagnosis.

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