Finding a breast lump can be unsettling, but most breast lumps aren’t cancerous. Very often, these lumps turn out to be fluid-filled cysts.

There are some characteristics that can help differentiate a cyst from a tumor. Even so, it’s important that you see your doctor about breast lumps so you can get the right diagnosis.

In this article we’ll explain some of the key differences between breast cysts and tumors, and how an ultrasound can help determine which one it is.

Breast cysts form when there’s a build-up of fluid. There may be a connection between cysts and fluctuating hormone levels, but the exact cause isn’t clear.

These round or oval fluid-filled sacs are fairly common. This is particularly true among people in their 40s who were assigned female at birth.

Cysts can be so small (microcysts) that you can’t feel or see them without breast imaging. Sometimes, they can grow quite large (macrocysts).

Symptoms may vary in severity during your menstrual cycle and may include:

  • lumpiness
  • tenderness
  • pain

Cysts can be simple, complex, or complicated:

  • Simple cysts. These cysts have smooth borders, thin walls, and are totally filled with fluid. They’re always benign. Cysts that form due to fibrocystic changes are simple cysts.
  • Complex cysts. Unlike simple cysts, complex cysts have irregular borders, thick walls, and some solid matter within the fluid. Most are benign.
  • Complicated cysts. These cysts are somewhere in between simple and complex. They don’t have thick walls, but they may have some solid matter within the fluid. Most are benign.

A tumor of the breast is a solid mass that can be cancerous or noncancerous.

Noncancerous breast tumors

Noncancerous breast tumors are made up of abnormal cells. They’re benign, which means that although they can grow, they can’t spread to other parts of your body.

The most common types of benign breast tumors include:

  • Fibroadenoma: These benign tumors are made up of connective and gland tissues. They’re most common in people between 20 and 30 years of age, and can be 1 to 5 centimeters in size. They can feel smooth or rubbery, with well-defined edges, and are easy to move with your fingers.
  • Intraductal papilloma: These tumors develop in the breast duct, usually near the nipple, and may cause pain.
  • Phyllodes tumor: These tumors start in connective and gland tissues. The lump may be round and firm, sometimes causing pain. They tend to be fast growing. Only a very small number of phyllodes tumors are cancerous.

Cancerous breast tumors

The cells of cancerous tumors contain damaged DNA. Instead of dying off, they produce more abnormal cells, forming tumors that can push into healthy tissue.

Cancer cells can also break off to form new tumors, or enter your bloodstream and lymphatic system. When this happens, the cancer cells can spread to distant organs.

Most breast cancers are adenocarcinomas — a type of tumor that develops in mucus-producing glandular cells. A ductal carcinoma starts in the milk ducts, and a lobular carcinoma starts in the milk-producing lobules.

Rare types of cancerous breast tumors include:

Early-stage breast cancer doesn’t always cause symptoms, but symptoms can include:

  • a hard, firm lump you can’t easily move with your fingers
  • a lump that doesn’t change with your cycle
  • changes to the size and shape of your breast or nipple

If you have a breast lump, it’s important that you have a doctor make the diagnosis as soon as possible. While there are some telltale differences between a cyst and a tumor, these differences can be subtle. Plus, there are always exceptions to these norms.

Likely features of a breast cyst

  • pain
  • feels soft and smooth
  • can be easily moved within your breast tissue
  • changes with your menstrual cycle

Likely features of breast tumor

  • no pain
  • feels hard and firm
  • can’t be easily moved within your breast tissue
  • doesn’t change with your menstrual cycle
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A physical exam can give your doctor a general idea of whether you’re dealing with a cyst or a tumor.

The next step is usually an ultrasound test.

If soundwaves pass right through the lump, that means it’s filled with liquid and is a simple cyst. If the soundwaves echo back, it means there’s at least some solid matter and more testing will be needed to reach a diagnosis.

If the ultrasound shows a complex or complicated cyst, the next steps may include:

  • a mammogram or MRI to get a better view of the entire breast
  • aspiration or draining the cyst with a fine needle to see if the fluid contains any blood or unusual cells.
  • a biopsy to determine if the solid areas are cancerous or benign

In an estimated 1.6 million breast biopsies a year in the United States, 75 percent are benign.

A simple cyst is no cause for concern and doesn’t necessarily need to be treated. Your doctor may suggest a “wait and see” approach because cysts sometimes go away on their own.

For cysts that continue to cause discomfort, your doctor can drain the cyst or surgically remove it.

According to the American Cancer Society, simple cysts don’t increase your risk of developing breast cancer, though there’s a small chance that complex cysts may.

A 2019 study found that 30 percent of breast cancer cases were in people who had a history of benign breast disease.

If you’re concerned about your breast cancer risk or have a family history of breast disease, talk with your doctor about how and when you should get screened, and if there are any other precautions you should take.

Early-stage breast cancer doesn’t usually cause symptoms, but here are some warning signs:

  • a breast lump
  • swelling, redness, or soreness of the breast
  • skin on the breast that’s dimpled, flaking, or thickened
  • nipple inversion or discharge
  • swollen lymph nodes under your arm or around your collar bone

Having some of these symptoms doesn’t mean you have breast cancer. But it does mean that you should follow up with your doctor. Breast cancer is easier to treat in the early stages, before it has the chance to spread to other parts of the body.

Performing a breast self-exam will help familiarize you with what’s normal for your breasts. This can make it easier to notice any changes that may occur later on. If you menstruate, the best time for a self-exam is a few days after your period has ended.

Follow these steps when doing a self-exam:

  • Stand unclothed in front of a mirror. Keep your shoulders straight with your arms at your sides. Look for changes in the size, shape, or color of your breasts. Also look for swelling and nipple changes, including discharge.
  • Repeat with your arms raised.
  • Next, lie down and lift your right arm over your head.
  • Use your left hand to check your right breast. Use the pads of your fingers, keeping your fingers flat and pressed together. With a firm touch and a small circular motion, feel for abnormalities in your breast, starting at the nipple, and spiraling outward.
  • Continue to examine your entire breast, from your collarbone to the top part of your abdomen, and from the center of your chest to your armpit. Try to follow a pattern so you cover your entire breast. Before you finish, gently squeeze your nipple to check for any discharge.
  • Finally, stand or sit up, lift your right arm over your head and massage your breast in a similar manner to the steps above. Doing this in a shower when your skin is wet may make it easier to feel your breasts.
  • Once you’re done with one breast, switch sides and repeat. Try to do a self-exam once a month, around the same time each month.

If you notice anything unusual, call your doctor. A breast exam doesn’t take the place of routine medical care and breast cancer screening.

See your doctor if you feel an unexplained lump in your breast or notice other changes, like:

  • changes to the skin on your breast
  • swelling
  • discharge
  • nipple inversion

During your visit, ask about your risk factors and recommended screening schedule.

A lump in your breast could be a cyst or a tumor. There are some characteristics to look for, including symptoms that change during your period, that could point toward one or the other.

Breast cysts are fluid-filled sacs. They’re quite common, especially for people in their 40s who were assigned female at birth.

Most of the time breast cysts turn out to be benign, and don’t need treatment. A tumor can be cancerous or noncancerous, and usually requires treatment.

It can be difficult to tell a cyst from a tumor by just feeling it or taking other factors into consideration. If you feel a lump of any kind in your breast, it’s important to follow up with your doctor for a proper diagnosis as soon as possible.