A phyllodes tumor is a rare tumor of the breast. Phyllodes tumors grow in the connective tissue of the breast, called the stroma. This includes the tissue and ligaments that surround the ducts, blood vessels, and lymph vessels in the breast.

The name “phyllodes” comes from the Greek word for “leaflike.” The name describes the pattern the cells of these tumors grow in, which looks like a leaf.

Less than 1 percent of all breast tumors are of this type.

About 90 percent of phyllodes tumors aren’t cancerous, so they don’t often spread outside the 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.

Doctors often confuse phyllodes tumors with a more common breast growth called a fibroadenoma. Fibroadenomas are hard lumps made up of connective tissue and tissue from the breast ducts. They aren’t cancerous. The main difference between the two conditions is that phyllodes tumors grow faster and start later in life.

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. The first sign is often a lump under your skin. The lump will feel smooth to the touch. The skin over your breast might also turn red 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.

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 see 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.

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 though 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.

A few different types of surgery are used to treat phyllodes tumors:

  • 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.

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

To catch the tumor if it does return, you’ll see your doctor for regular follow-ups. 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.