What breast cysts are
A breast cyst is a round or oval, fluid-filled sac that forms within the breast tissue. Cysts feel smooth and may move slightly when pressed. They can be single or multiple, in one breast or both, and can range from a few millimetres to several centimetres in size. They are extremely common, particularly in women aged 35 to 50.
Breast cysts form when fluid accumulates inside the breast lobules (milk-producing glands). Hormonal changes during the menstrual cycle influence how they behave, and many women notice their cysts change in size or tenderness at different points in the month.
Types of breast cysts
Breast cysts are broadly classified based on their appearance on ultrasound:
- Simple cysts: entirely fluid-filled with smooth walls and no internal structure. These are almost always benign and need no treatment unless painful.
- Complex or complicated cysts: contain some internal debris, thickened walls, or solid-looking areas. These require more careful assessment but are still most often benign.
Symptoms
Many breast cysts are found incidentally on imaging and cause no symptoms at all. When symptoms do occur, they typically include:
- A smooth, moveable lump that you can feel in the breast
- Tenderness or aching in the breast, especially before a period
- A lump that changes size with the menstrual cycle, often larger before a period and smaller after
How breast cysts are diagnosed
Ultrasound is the main imaging tool for breast cysts. It clearly distinguishes between fluid-filled cysts and solid lumps. In younger women, ultrasound is usually the first investigation. In women over 40 or post-menopause, a mammogram may also be done to look at the overall breast picture.
A doctor can usually distinguish a cyst from a solid lump during clinical examination, but imaging confirms the diagnosis with certainty.
When treatment is needed
Simple cysts that cause no symptoms are watched and do not need treatment. They often resolve on their own after a menstrual cycle or two. Treatment is considered when:
- The cyst is large and causing discomfort or distortion
- The cyst is painful and interfering with daily life
- The cyst has complex features that need further investigation
- The cyst is rapidly enlarging
Aspiration vs surgery
The standard treatment for a symptomatic breast cyst is aspiration, where a fine needle is inserted under ultrasound guidance and the fluid is drained. This takes a few minutes, is done in the outpatient setting, and gives immediate relief. The cyst may refill over time, in which case repeat aspiration can be done.
Surgery is rarely needed for breast cysts. It may be considered if aspiration repeatedly fails, if the cyst keeps refilling with blood-stained fluid, or if the imaging and cytology findings raise doubt about the nature of the lesion.
Finding a breast cyst can be frightening, but the vast majority of cysts are not cancer. Getting a proper assessment quickly gives you a clear answer and peace of mind.
When to seek urgent assessment
See a specialist promptly if a cyst is rapidly growing, if the fluid drawn during aspiration is blood-stained, or if there is a solid component visible on ultrasound. These features do not mean cancer is present, but they do need further evaluation to be certain.