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What are breast cysts?

Breast cysts are fluid-filled round or oval sacs, similar to blisters, that form within the breast. They are usually benign (noncancerous). In most cases, breast cysts do not require treatment unless they are large and painful or uncomfortable.

Breast cysts are common in women. Although they can develop in women of any age, they are more common in women aged 35 to 50, and in women taking hormone replacement therapy. Breast cysts can also be found in men, although this is very rare.

What causes cysts in breasts?

Breast cysts develop when fluid accumulates inside the  milk glands of the breasts. The exact causes of why this occurs is not known. Cysts may develop due to hormonal changes arising from a woman’s monthly menstrual cycle.

What does a breast cyst feel like?

Breast cysts may be found in one or both breasts. If you have a breast cyst, you may feel:

  • A smooth, easily movable lump under the skin
  • Breast pain or tenderness in the area of the breast lump

If you notice any new or unusual breast change, please speak with your doctor without delay. Most breast changes are not caused by cancer, however some lumps may not be cysts and will require further investigation.

Do breast cysts hurt?

Most cysts are tiny (only a few millimetres in diameter). They are too small to be felt and cause no symptoms, although they may be seen during imaging tests such as a mammogram or ultrasound. These cysts are also referred to as microcysts.

If fluid continues to accumulate, large cysts (also called macrocysts) can form, which can cause pain and discomfort. Large cysts can grow to about 1 to 2 inches in diameter (2.5 cm to 5 cm). If the cyst causes pain, you and your doctor may decide to have it drained to ease symptoms.

When to see your doctor

If you notice any new or unusual changes in your breasts, please speak to your doctor without delay. This includes breast changes such as a new lump, a lump that grows or persists, or changes on the skin of the breast.

Most breast changes are not caused by cancer. However, it is important to speak with your doctor so that the breast change can be checked. Even if you have been diagnosed with breast cysts before, it is important that every new breast lump be checked as some lumps may not be cysts and will require further follow up.


Diagnosis of a breast cyst

Diagnosis of a breast cyst usually involves a breast exam, imaging tests (such as a breast ultrasound or mammogram), and possibly a breast biopsy.

  • Breast exam – your doctor will physically examine the breast lump and check the breast for other abnormalities. However, cysts cannot be reliably diagnosed by physical exam alone. You may need another test, such as an imaging test or a biopsy to confirm the diagnosis.
  • Mammogram – breast cysts are often found during routine mammograms to screen for breast cancer. On a mammogram, they can sometimes be seen as a smooth round mass in the breast tissue.
  • Ultrasound – this imaging test helps your doctor to see if the lump is solid or filled with fluid. If the lump is filled with fluid, this usually indicates a cyst (also called a simple cyst). Simple cysts are not usually a cause of concern. However, if the lump is solid or has a combination of solid and fluid components (called a complex cyst), your doctor may recommend a biopsy to ensure the lump is not cancerous.
  • Breast biopsy – Because solid lumps could indicate breast cancer, your doctor may recommend doing a biopsy, such as a fine-needle aspiration (FNA). During a fine-needle aspiration, a thin, hollow needle attached to a syringe is inserted into the breast lump to withdraw (aspirate) fluid and tissue. This is often done with an ultrasound to guide accurate placement of the needle. A local anaesthetic may be used to numb the area where the needle will be inserted. A sample of the fluid may be sent to a pathologist to confirm the diagnosis.

Breast Cyst Treatment Options

No treatment is needed for simple cysts (those that are fluid-filled) that cause no symptoms, after the diagnosis is confirmed by ultrasound.

If ultrasound indicates that the cyst contains a solid component (a complex cyst), a biopsy may be needed to exclude the possibility of cancer. However, some doctors may recommend that the cyst be monitored closely by ultrasound, particularly if the solid components are small.

If the cyst is large or causing discomfort, fine-needle aspiration can be used to remove fluid from the cyst to ease symptoms.

Cysts that are drained can come back or new cysts can form in nearby tissue. It is possible to drain the cyst again.

Occasionally, surgery can be recommended to remove cysts, although this is uncommon. Surgery is usually only reserved for cysts that continue to come back and cause symptoms, or cysts that show worrisome features in imaging or pathology tests.

Breast Cysts and Cancer

In general, cysts are usually not cancerous. Simple cysts are not breast cancer and do not change into cancer. In very rare cases, cysts may have cancer growing within or close to them, which can usually be found by ultrasound or by biopsy.

Having simple cysts does not increase the risk of breast cancer in the future. However, there is a small chance that complex cysts may contain cancer or increase your breast cancer risk later, depending on what is found in the biopsy.

People who develop a lot of cysts may become complacent about breast lumps and not have breast lumps checked. This can result in a delayed diagnosis if breast cancer develops. Even if you have been diagnosed with breast cysts before, please see your GP If you notice a new breast lump, changes on the skin of the breast over the cyst, or other unusual breast changes, even if you think it may be a cyst or your cyst has returned. Early detection gives the best chance of survival if you are diagnosed with breast cancer.

Questions you can ask your doctor

Ask your doctor to take a closer look at any new or unusual breast changes that concern you. However, being specific about your particular concern can be helpful. For example, clearly stating which part of the breast is affected and how long you have noticed the change.

Some questions you might like to have ready if you see your doctor about your breast change:

  • What can you feel in my breast(s)?
  • Which tests do I need to check a breast lump?
  • When will I get the results?
  • What were the results of my tests?
  • Will I need a biopsy (using a needle to remove a small amount of breast tissue so it can be examined under microscope)?
  • If more tests/treatment is needed, will you refer me to a breast specialist?
  • What do I do if the cyst comes back after it has been drained (aspiration)?
  • Do you have anything I can take away with me to read more about this? What websites do you recommend?

Words: Francesca Brook
Reviewed by NBCF Research team.