Phyllodes tumors are a rare type of breast tumor. The pattern of their cells resembles leaves, and the name "phyllodes" comes from the Greek word meaning "leaf-like."

Phyllodes tumors can grow quickly, but they do not always spread beyond the breast.

Authors of a 2013 review note that 35–64% of phyllodes tumors are benign, with the rest being borderline or malignant. According to the American Cancer Society, around 25% are malignant.

Although many of these tumors are benign, a doctor may recommend surgery to reduce the risk of further development.

Phyllodes tumors can form at any age, but they tend to affect women aged 35–55 years. Those that develop in younger women are more likely to be benign.

Very rarely, phyllodes tumors develop in males, usually in those with a condition called gynecomastia.

a woman getting a mammogram to check for phyllodes tumorsShare on Pinterest
A mammogram is one way to screen for phyllodes tumors.

The most common indication of a phyllodes tumor is a breast lump that is easy to feel. These lumps often form in the upper outer quadrant of the breast.

Phyllodes tumors tend to grow quickly. In a few weeks or months, a tumor can reach at least 2–3 centimeters (cm). The average size is around 4 cm, but they can be several times larger. Around 20% of phyllodes tumors exceed 10 cm in diameter.

This type of tumor is not usually painful. It can become visible as it pushes against the skin of the breast, and it may expand the veins under the skin, causing that area of the breast to appear blue.

The tumor may cause an ulcer to form on the skin of the breast, but this is rare. An ulcer can form whether the tumor is benign, borderline, or malignant.

Phyllodes tumors can form in both breasts, but this is very rare.

Phyllodes tumors are rare — they make up 0.3–0.5% of breast tumors in women. As a result, doctors are less likely to encounter them, which can make diagnosis more difficult.

Also, a phyllodes tumor can look like a type of solid breast growth called a fibroadenoma. A fibroadenoma is a benign, growing lump of regular breast cells.

Fibroadenomas are the most common type of breast mass, and they often develop in younger women.

Some researchers have suggested that phyllodes tumors may be a type of fibroadenoma. However, there are two main differences between these types of tumors.

First, phyllodes tumors tend to grow more quickly than fibroadenomas. Second, phyllodes tumors tend to develop about 10 years later, when people are in their 40s. Fibroadenomas tend to appear when people are in their 20 and 30s.

These distinctions can help a doctor make an accurate diagnosis.

Imaging

As with other tumors, diagnosing a phyllodes tumor may involve:

A mammogram: The results will show a roundish mass with well-defined edges. In some cases, rounded lobes may appear within the tumor.

An MRI or ultrasound: These imaging tests can provide more detail.

Find out more here about what a mammogram involves.

Biopsy

Only a breast biopsy can confirm whether the mass is a phyllodes tumor.

A biopsy involves taking tissue samples for testing. These tests provide confirmation of the type of tumor.

A doctor may recommend a core needle biopsy or an excisional biopsy. A core needle biopsy involves the doctor taking a sample through the skin, using a hollow needle. This may not provide enough evidence that the mass is a phyllodes tumor.

An excisional biopsy involves a surgeon removing the whole tumor for testing. Examining the whole tumor can lead to a more accurate diagnosis.

Beyond confirming the type of tumor, a biopsy can help determine whether a tumor is benign, borderline, or malignant.

Identifying a tumor

Features of a benign tumor include:

  • well-defined edges
  • cells that do not divide rapidly
  • connective tissue cells that do not look unusual
  • no overgrowth of connective tissue cells

Features of a malignant tumor include:

  • irregular edges
  • cells that seem to be dividing rapidly
  • overgrown connective tissue cells with an unusual appearance

Borderline tumors have features of the benign and malignant forms.

Malignant tumors — particularly those with lots of connective tissue overgrowth — may spread and grow quickly, possibly spreading beyond the breast.

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Surgery can remove a phyllodes tumor.

The only way to treat a phyllodes tumor is to remove the growth entirely.

This can help prevent additional tumors from forming and prevent the existing tumor from causing complications, whether it is benign or cancerous.

The surgeon will remove the tumor and at least 1 cm of surrounding tissue to reduce the chances of the tumor growing back.

If the tumor is cancerous, the surgeon may remove more of the surrounding tissue.

At this stage, radiation therapy and chemotherapy are unlikely to help with a cancerous phyllodes tumor, and these tumors do not respond to hormone therapy.

If a cancerous phyllodes tumor recurs, a doctor may recommend a mastectomy, surgery to remove part or all of the breast. They may also recommend radiation therapy, chemotherapy, or both.

Although benign phyllodes tumors may not spread beyond the breast, they need treatment to prevent them from growing larger. Otherwise, the lump can become visible and break through layers of skin, causing pain and discomfort.

Effect on cancer risk

If a malignant phyllodes tumor recurs, there is a limited risk of this type of tumor developing beyond the breast. Only 5% of all phyllodes tumors recur elsewhere the body, according to Breastcancer.org.

Having a benign phyllodes tumor does not increase the risk of developing cancer, including breast cancer.

After the removal of a phyllodes tumor, a person may experience pain at the site of the surgery, but further complications are rare.

Benign phyllodes tumors are less likely to recur than malignant ones. The doctor will monitor for recurrence, usually within 1–2 years after removal.

The Genetic and Rare Diseases Information Center note that the outlook for people who undergo surgery for benign phyllodes tumors is excellent.

Without treatment, however, even benign tumors can cause complications. For this reason, anyone who notices any breast-related changes should seek medical attention.