The short answer: You will usually get a breast ultrasound, because a cyst and a solid mass can look the same on a mammogram, per the American Cancer Society (2026). A simple cyst rarely needs treatment. A complicated cyst may need follow-up imaging or fluid testing. A complex cyst usually needs a core needle biopsy.

A report that names a cyst is common. A 2010 radiology review calls cysts the most common type of breast mass, with a peak between ages 35 and 50. In one trial of high-risk women, ultrasound found cysts in 998 of 2,659 women (37.5%) at the first screening. This guide covers cysts only. For recalls in general, see our mammogram callback guide.

Why can't a mammogram alone tell a cyst from a solid mass?

A mammogram shows the outline of a mass. It does not reliably show what is inside. The American Cancer Society says a cyst and a solid mass can look the same on a mammogram. The 2010 review agrees, with one exception: large cysts that contain calcium.

So why might your report already say "cyst"? The usual reasons:

  • Calcium in a cyst. Calcium can settle in the fluid. It then changes shape between views, and a side view shows it in a layer.
  • An oil cyst. This fat-filled cyst has a look that is specific on a mammogram. The American College of Radiology lists it as a definite benign finding.
  • Many masses in both breasts. At least 3 masses, with at least 1 in each breast, can be called benign if none looks suspicious. Cysts are a usual cause.

If the report says "possible cyst" or "mass," the radiologist does not yet know what it is.

What does the breast ultrasound show?

Ultrasound is best at showing whether a mass is solid or filled with fluid. It can also classify a finding that a mammogram alone cannot interpret well. If you are 30 or older with a lump, you will usually have both tests.

A classic simple cyst has a clear look on ultrasound. The 2010 review describes an oval or round shape, dark and fluid-filled inside, with no blood flow and no visible wall. A cyst also tends to flatten under gentle pressure, unlike most solid masses.

Ultrasound can find cysts as small as 2 to 3 mm. In one observer study, though, reliable description varied until cysts reached at least 8 mm. MRI can also show cysts, but these sources describe ultrasound as the usual next test. For how that scan works, see mri.md.

How are simple, complicated, and complex cysts handled?

The look of the finding sets the category and the plan. Our BI-RADS guide explains the numbers.

  • Simple cyst. This is fully fluid-filled and is not a cause for concern. It is usually rated BI-RADS 2 (benign). You usually go back to routine screening.
  • Complicated cyst. This looks like a simple cyst but has debris in the fluid. The debris is protein from cell turnover, blood, or pus. If the debris moves or forms a level, it is BI-RADS 2 with no follow-up needed. If the debris is even and the finding is isolated, it can look solid. It is then usually BI-RADS 3 (probably benign), with imaging at 6, 12, and 24 months.
  • Clustered microcysts. These are tiny cysts in a group. They are a common benign finding before and around menopause. After menopause, a short-term follow-up may make sense.
  • Complex cyst. This has a thick wall, thick internal divisions (0.5 mm or more), a mass inside, or solid parts. It is usually BI-RADS 4 (suspicious), and a core needle biopsy is usually needed.

The risk differs a lot between these groups. Across 6 earlier series, 2 of 868 lesions (0.23%) thought to be complicated cysts were cancer. In the same review, 97 of 270 complex cystic and solid lesions (36%) were cancer. A 2003 study in Radiology found 18 of 79 (23%). So many complex cysts are benign, but imaging alone often cannot show which ones.

A study of 175 symptomatic cystic lesions found the same split. All 95 simple, clustered, thin-septated, and complicated cysts were benign. Of the 80 lesions with solid parts or thick walls, 40 were cancer. This was a selected group, so the rates do not apply to every cyst.

When is aspiration or biopsy used?

Aspiration means a thin, hollow needle removes the fluid. It has three main uses:

  • To settle an unclear ultrasound. If the mass disappears after the fluid comes out, it is most likely a cyst.
  • To ease pain. The ACR says aspiration can be considered for symptomatic relief of a palpable simple cyst. A cyst drained for pain can still be BI-RADS 2.
  • To check a tender cyst. The 2003 study concluded that symptomatic complicated cysts generally warrant aspiration. A possible abscess also calls for it.

Cyst fluid is usually clear or cloudy, and yellow or greenish black. The 2010 review says this fluid can be discarded. Bloody fluid or pus is different: the team should test bloody fluid in a lab. Even so, the review says the risk of cancer in that case is very low.

Sometimes no fluid comes out. Across 3 series, 64 of 517 lesions (12%) thought to be complicated cysts turned out to be solid. Of those 64, 2 were cancer. A solid result can lead to a biopsy.

Biopsy removes tissue, not only fluid. For complex lesions, the review says aspiration alone is unlikely to give a diagnosis. Ultrasound guides a core needle to the solid part. The team may place a small marker clip at the site.

What happens next, step by step?

This is the usual path. Your own team may change the order.

  1. Read the result. BI-RADS 0 means the exam is incomplete and more imaging or a comparison with past images is needed. It does not mean cancer.
  2. Book the diagnostic visit. Ask the imaging center if it has your past mammograms. Tell the team about any lump, pain, or hormone therapy.
  3. Get ready for the ultrasound. The exam needs little or no preparation. Wear loose, comfortable clothes and leave jewelry at home.
  4. Get the imaging. Expect extra mammogram views, an ultrasound, or both.
  5. Hear the category. Ask for the finding's name (simple, complicated, or complex) and its BI-RADS number.
  6. Follow the plan for that category. This means routine screening, short-interval imaging, aspiration, or a core needle biopsy.
  7. Get the next date in writing. Ask when your next imaging is due.
  8. Report changes. Tell your doctor about any new breast change, even if a mammogram is not due.

What follow-up is normal after a cyst?

Cysts come and go, so a change alone is often expected. In one series of 68 new benign cysts, 47% were gone within 1 year and 69% within 5 years. They also can change with the menstrual cycle, and they are often largest just before a period.

For BI-RADS 3, the American Cancer Society says repeat imaging in 6 to 12 months and regularly after that. This usually lasts at least 2 years. Findings in this group have no more than a 2% chance of being cancer.

Slow growth is not always a problem. The 2010 review accepts growth of 20% or less in diameter over 6 months for complicated cysts. Faster growth or new suspicious features can move it to BI-RADS 4, with aspiration and possible biopsy.

Most cysts do not change your risk. The National Cancer Institute says most are benign and do not increase your risk of breast cancer. A recall that ends this way is one kind of false positive. You still go back to routine screening.

The bottom line

A mammogram can raise the question, and ultrasound usually answers it. Simple cysts are benign and usually need nothing more. Complicated cysts usually mean watching or draining. Complex cysts usually mean a biopsy, and many of those are still benign. Ask for the exact name of your finding and its BI-RADS number.

Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Ask your doctor or radiologist what your own report means and what follow-up you need.