How do you tell if it’s a breast cyst or a tumor?

Feeling a lump in your breast understandably leads to worry and panic. Is it a harmless cyst? Or could it be a sign of breast cancer? One thing is for sure: you want your uncertainty addressed. So how do you tell if it’s a breast cyst or a tumor?

“If you feel a lump of any kind, it’s important to get it evaluated,” says Dr. Correna Terrell, breast radiologist at Houston Methodist.

“It’s not unusual for a woman to discover a breast cyst at some point in her life, but we never want to miss a breast cancer diagnosis.”

From what a breast cyst feels like to how a radiologist can tell the difference between a cyst and a tumor, here’s everything you need to know if you’ve discovered a lump.

What are the causes of breast cysts?

“A breast cyst is a round or oval sac in the breast that is filled with fluid,” explains Dr. Terrell. “The exact cause is unknown, but breast cysts are thought to be related to natural fluctuations in hormone levels.”

Although they can appear at any age, breast cysts are quite common in women between the ages of 35 and 50. They can vary in size – as small as a grain of rice or as large as a golf ball – and a woman can sometimes have more than one. Breast cysts are almost always benign (noncancerous) and do not require treatment unless the cyst is large and needs to be drained.

On the other hand, a breast tumor is a solid mass – rather than a fluid-filled sac. They can be benign or malignant (cancerous).

“A malignant breast tumor always requires treatment,” he says Dr. Terrell. “The earlier we detect breast cancer and start treatment, the better – which is why any lump or change in the breast should be evaluated.”

What does a breast cyst feel like?

You may wonder if there are any breast cyst symptoms, such as breast tenderness or pain, that can help you distinguish between a harmless lump and a potentially cancerous one. But it is not that simple.

“There are some differences between a breast cyst and a tumor, but they can be subtle—and there are always exceptions,” says Dr. Terrell. “It can be difficult to tell a cyst from a tumor just by palpation.”

That said, a breast cyst is more likely to:

• Be painful or tender
• Feel soft and smooth, like a water balloon (although sometimes they can feel firm)
• Be easy to move
• Change with the menstrual cycle (grow and decrease in size or tenderness)

“A breast lump is usually painless, firm, difficult to move and will not change with the menstrual cycle,” says Dr. Terrell. “But while these features can give some indication of whether it’s a cyst or a tumor, the only way to accurately assess a nodule is through imaging.”

Breast cyst vs. tumor: How to tell if a lump is cancerous

If you feel a lump in your breast of any kind, it’s important to get it evaluated – which includes mammography (depending on age) and ultrasound.

“A radiologist can tell the difference between a cyst and a tumor with a breast ultrasound,” says Dr. Terrell. “A cyst will have smooth walls and be filled with clear fluid, while a tumor will have a solid appearance.”

A small, simple breast cyst usually doesn’t need treatment and should go away on its own over time. Alert your doctor if it persists for several menstrual cycles or becomes painful. A large cyst may need to be drained by fine needle aspiration, especially if it is painful.

If a breast lump appears solid and has suspicious features on a mammogram, your radiologist will recommend a biopsy to further evaluate the mass and determine whether or not it is cancerous. Some solid nodules with benign features on ultrasound may be monitored with follow-up ultrasound examinations.

Can a breast cancer be misdiagnosed as a cyst?

A clinical breast exam is part of diagnosing a breast lump, but again, it can be difficult to tell a cyst from a tumor just by palpation. This is why ultrasound is an essential component in evaluating a nodule. Depending on your age, it may also be a mammogram.

“Without imaging, a breast lump can certainly be misdiagnosed and cancer could potentially be missed,” says Dr. Terrell. “Any new lump or change in breast tissue should be evaluated by a breast radiologist who has the tools and technology to provide an accurate diagnosis.”

Can a breast cyst turn into a tumor?

A benign breast cyst cannot become cancerous and turn into a tumor. But although rare, breast cysts are not always benign.

“Complex cysts—those with irregular borders, thick walls, and some solid material within the fluid—have a 20-30 percent chance of being malignant,” adds Dr. Terrell. “This is when we would recommend either a biopsy of the cyst so we can rule out breast cancer or an imaging check in a few months.”