A phyllodes tumor is a rare tumor of the breast. Phyllodes tumors grow in the connective tissue of your breast, called the stroma.

The American Cancer Society says that most phyllodes tumors aren’t cancerous, so they don’t often spread outside your breast. However, they can grow quickly. Some phyllodes tumors are between benign and cancerous. These types are considered “borderline.”

Though you can get one of these tumors at any age, they’re most common in women who are in their 40s. You’re more likely to get a phyllodes tumor if you have a rare, inherited genetic condition called Li-Fraumeni syndrome.

The cause of phyllodes tumors is unknown. They may just arise as people age.

Several factors may be involved in causing these tumors to grow, including:

  • injury
  • breastfeeding
  • pregnancy
  • increased levels of estrogen, a female hormone

Phyllodes tumors grow very quickly. Breastcancer.org says that the first symptom is often a lump under your skin. The lump will feel smooth to the touch. The skin over your breast might also turn red or discolored and feel warm. The tumor may grow quickly enough that you can eventually see it under your skin.

Even though most phyllodes tumors aren’t cancerous, they can grow and cause pain. If the tumor breaks through your skin, you might see an open sore on your breast.

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Illustration by Maya Chastain

Phyllodes tumors can be hard to diagnose. They look very similar to other breast lumps, such as fibroadenomas.

You might first feel the lump while doing a breast self-exam. If you do find a lump, it’s important to call a doctor as soon as possible, because these tumors grow so quickly. Your doctor can do tests to confirm whether you have a phyllodes tumor.

First, the doctor will do a clinical breast exam. They’ll check the shape and size of the lump.

The Genetic and Rare Diseases Information Center says that you can have one or more of these tests to confirm that you have a phyllodes tumor:

  • A mammogram uses X-rays to take pictures of your breasts.
  • An ultrasound uses sound waves to create pictures of your breasts.
  • An MRI scan uses powerful magnets and radio waves to produce cross-sectional pictures of your breasts.
  • A biopsy involves removing a piece of the tumor through a hollow needle, or the whole tumor through a cut in your skin.

To tell for sure if you have a phyllodes tumor or a fibroadenoma, your doctor will most likely have to remove the whole tumor. The tumor goes to a lab, where pathologists look at it under a microscope. If the tumor is noncancerous, the edges will be well-defined and the cells won’t divide quickly.

Even when a phyllodes tumor is benign, it can grow and cause pain and other problems. Your doctor will recommend that you have surgery to remove it. The surgeon will remove not only the tumor, but also some of the healthy tissue around it.

Breastcancer.org says that a few different types of surgery are used to treat phyllodes tumors. The type of surgery a person may receive depends on the size of the tumor and the patient’s preferences.

  • Lumpectomy. The surgeon removes the tumor, along with at least 1 centimeter (0.4 inches) of tissue around it. Removing this extra tissue helps prevent the tumor from coming back.
  • Partial mastectomy. If the tumor is larger, the surgeon will remove the entire part of the breast that contains it.
  • Total mastectomy. The surgeon removes the whole breast. You can have breast reconstruction surgery at the same time, or after the mastectomy.

If the tumor is cancerous, your doctor may recommend these treatments:

  • Radiation uses high energy waves to kill cancer cells. Your doctor can use it after surgery to treat a cancerous phyllodes tumor that hasn’t spread outside of your breast.
  • Chemotherapy uses chemicals to kill cancer cells throughout your body. This treatment is an option if a cancerous tumor has spread to other parts of your body.

A phyllodes tumor can recur whether it was cancerous or not. A cancerous tumor may recur more quickly than a noncancerous tumor. If there is a recurrence, Breastcancer.org says that it typically happens between 1 to 2 years after the initial surgery.

Your doctor will want to watch you closely after the removal of the initial tumor. A doctor will typically follow up with regular breast exams, mammograms, ultrasounds, and possibly MRIs. If a cancerous tumor comes back, a doctor may recommend a mastectomy. There is a small chance that the tumor will recur in other parts of the body aside from the breast.

Phyllodes tumors aren’t usually cancerous, but they can sometimes return after treatment. Usually, these tumors come back within 1 or 2 years after you have surgery. Cancerous tumors may come back sooner.

To catch the tumor if it does return, you’ll schedule appointments with your doctor for regular follow-ups. It is also important to do breast self-exams. You’ll have clinical breast exams every 4 to 6 months. You’ll also need routine imaging tests like mammograms, ultrasounds, and MRIs to check for a return of the tumor in the affected breast.