Mass characteristics of breast cancer on mammograms

Typical ‘mass’ findings at first screening for breast cancer

A mammogram is an X-ray of the breast. If anything curious is revealed, usually appearing as a ‘shadow’ of some kind, the next thing is probably an ultrasound, and also a careful clinical exam. A biopsy may or may not be requested at the mammogram stage, or may be delayed until the ultrasound confirms a mass, or the mammogram characteristics plus palpable features are suggestive of a mass.

David David
What do radiologists do when they see a nodule?

So, there are typical steps that radiologists usually recommend when a mammogram shows a possible ‘mass’. The radiologist might arrange for magnified mammogram views to look for microcalcifications, or might arrange for breast ultrasound to be done, to see if it is actually a cyst, and not a solid mass.

Dr. Halls Dr. Halls
Hopefully ultrasound shows just a cyst.

If multiple solid nodules are found, it increases the changes that it is not cancer.

Megan Megan
Why is multiple nodules good?

Dr. Halls Dr. Halls
Because benign fibroadenomas tend to be multiple, cancer tends to be single.

If cysts are found, they are definitely not cancer.
If the radiologist think the mass is solid, based on its shape on the mammograms or based on the ultrasound results, then it might need a biopsy.

The breast mammogram below certain appears to have a nodule of some sort, but since it may or may not be a real nodule, one could label it as an ‘asymmetric density’ or a ‘developing asymmetry’.

Dr. Halls Dr. Halls
Notice the whitest spot, near the bottom of the image? That’s the possible nodule, but we won’t know for sure if its real, solid or cyst, until we get an ultrasound.

When a mass is seen on one mammogram view, the radiologists wonders, is it only one ‘view’? If so, it may be called ‘asymmetric density’. The radiologist must look at both views, (They call them ‘orthogonal’ views. Orthogonal views are views from different angles, usually at 90 degrees, like looking at a face from the front and side )

A mass seen in both orthogonal views will be considered a ‘true’ mass.

Other curious findings which lead to a speculation of ‘unconfirmed mass’ include asymmetrical breast tissue, and architectural distortion, and these uncertainties will need to be resolved.

Brittany Brittany
What is asymmetrical breast tissue, and why?

Dr. Halls Dr. Halls
Only super-models are perfectly symmetrical. Everyone else is a bit different on each side of the body. So when we see an asymmetry, we don’t yet know if it’s normal or not.

Ultrasound is usually used, along with physical exam, to confirm an actual mass. If there is no confirmed mass, it might be called a ‘pseudo-mass‘,or a ‘composite shadow from overlapping structures’, and no further evaluation is required. If there is a mass, additional mammogram views and ultrasound are usually performed, followed by either biopsy or, if cancer seems unlikely, follow-up imaging in 6 months.

What does it mean if you have a ‘cyst’?

A cyst is a ‘fluid-filled‘ cavity of some kind. Breast cysts are very common and of no risk of cancer whatsoever. A cyst is like a water balloon, meaning fluid on the inside and a thin membrane around the outside. On a mammogram, a cyst looks like a round blob, but a round shape could be a tumor too. The smooth, round shape of a cyst wall gives a hint on the mammogram, but ultrasound is needed to make sure it is just a cyst. Sometimes there are suspended particles in the fluid, and these appear as ‘echoes’ on the ultrasound. This creates a bit of uncertainty as to whether or not it is ‘just fluid’, because these echoes can make it appear to be solid.

A screening finding of a simple cyst

A simple cyst is the most common mammographic pseudo-mass found at screening. Breast cysts tend to effect women in the 30-50 age range, and are uncommon in post menopausal women. They often form in the lobule from a distended acini. Most breast cysts are the result of fibroadenoma or breast fibrocystic disease, which are completely benign.

Dr. Halls Dr. Halls
Hey, that small dark round cyst on the ultrasound image, has a few speckles in it. But the margins are smooth enough, and it’s small enough, to just call a cyst.


On a mammogram a cyst is typically round or oval and with a well circumscribed margin. They can appear alone or in small groups, and may disappear over time or change in size. Simple breast cysts may also show rim-like calcifications. On the ultrasound a cyst will be anechoic featuring smooth, well defined walls. Ultrasounds are up to 100% accurate in determining simple breast cysts, unless there are particles of some kind floating in the fluid. A simple cyst is considered BIRADS category 2.

Clustered Microcysts and Complicated Cyst

Floating particles in a cyst are formally referred to as ‘clustered microcysts’. On the ultrasound they will appear as very small anechocic dots, each smaller than 2-3 mm, with no discrete solid components. These tiny foci have very thin septations between them ( less than 0.5 mm). The radiologist will be looking to differentiate potentially complicated cysts from apocrine metaplasia, or other more common fibrocystic changes.

A ‘complicated’ cyst is curious term based on the ‘complicated‘ ultrasound appearance. What makes it complicated is that something besides pus or blood may be responsible for the small echoes on the ultrasound. The cause of the echoes could be increased fluid levels, floating debris, or swirling echogenic foci (particles). Aspirated fluid samples will typically appear green, yellow, or milky-clear.

A complicated cysts will not appear to have a thickened wall or any solid mural nodules.
Complicated cysts and clustered microcysts are considered ‘probably benign’ if they are non palpable. That would correspond to a “BIRADS category 3, and given short term followup. If the lesions are palpable they will probably be aspirated (drained with a needle), and probably have a biopsy done as well.

Palpable complicated cysts and clustered microcysts are considered BIRADS category 4.

Complex cystic mass

Sometimes the differences between cystic lesions are subtle and vague. Quite recently, the term ‘complicated’ cystic mass and ‘complex’ cystic mass, were separated, even though semantically they mean just about the same thing. A ‘complex’ cystic mass is one that contains both fluid components AND solid components. These solid features could present as either a thickened lesion wall, or as solid mural nodules. Whether palpable or not, all complex cystic masses will require biopsy to figure out what is going on. A complex cystic mass corresponds to BIRADS category 4 or 5.

Asymmetric Density of a suspected mammogram image

An asymmetric density means that some sort of ‘opacity’ ( shadow- or something making it more difficult for light to pass through )is visible, but on only one projection. Additional projections from other angles attempt to confirm that the shadow was not just incidental. Sometimes the opacity is seen on two views, but lacks the convex-outward borders that are typical of a true mass, and this situation is still termed ‘asymmetric density.’
Ultrasound is also used as a followup evaluation, as well as ‘spot compression’ X-rays. Note that all mammograms are done with some breast compression, but a spot compression test uses a special plate or cone which lets you see a clearer image of a much smaller area. Margins also become clearer using spot compression.

Global asymmetry, focal asymmetry, developing asymmetry

When there is asymmetric density on a mammogram image, it can mean that a mass is developing, but it is far more likely that it is something else. There are different types of asymmetry; global, focal, and developing, and the chances of malignancy, though low, tend to increase if there are new developments from previous mammograms, and if the lesion is or become palpable.
Global asymmetry means that the area of increased density includes a significantly large portion of the breast. In most cases this is the result of normal variations in hormone levels. However, if something is palpable, the possibility for malignancy is as high as 10%, and the lesion will require further evaluation. Now, if the lesion appears to be a solid mass, or has suspicious microcalcifications, or an architectural distortion, then a biopsy will be required.

Focal asymmetry means the suspected asymmetry-mass is much smaller, and has a similar shape on two views. It lacks the clear borders that we see in a true mass, and it usually is found to be an ‘island’ of normal , yet dense fibroglandular tissue, especially when it is interspersed with fat. The liklihood of malignancy with focal asymmetry is less than 1%.
Followup procedures will to some degree depend upon whether or not this a first or subsequent screening. If there are previous mammograms and the focal asymmetry seems to be stable, then it is considered benign and yearly screenings are adequate. If this is the first screening and without other worrisome features, the lesion is ‘probably benign’ or about a BIRADS category 3. Short term ( 6 months or less ) follow up is recommended, but the chance of malignancy is still less than 2%.

A developing asymmetry is a focal asymmetry which is new, more dense, or larger than on a previous mammogram. The likelihood of malignancy is quite high, between 10-15%, and additional evaluations are always required at screening. A biopsy will likely be required if the lesion now seems ‘indeterminate’ as compared to previous screenings. If there are suspicious microcalcifications, evidence of a solid mass, or architectural distortion, a biopsy is always performed.

Brittany Brittany
What if I feel a lump, the mammogram only showed asymmetric density, and no ultrasound was ordered?

Dr. Halls Dr. Halls
You should ask your doctors for an ultrasound.

Brittany Brittany
What if ultrasound can’t find anything wrong?

Dr. Halls Dr. Halls
If YOU can feel a lump, for sure, remember this: sometimes mammograms and ultrasound fail to find masses. There is ONE MORE OPTION: You can ask your doctor to do a fine needle biopsy, by aiming the needle at the spot, guided only by feeling it with fingers.


Differential Diagnosis for a solitary, well-circumscribed mass

A suspected breast cancer ‘mass’ is a ‘space-occupying’ lesion seen on at least two mammogram projections, which also tends to be more dense in the middle than at the edges. Masses tend to be described according to their shape, margin, and density. ‘Density’ more or less refers to the amount of fat tissue in the mass when compared to the surrounding breast tissues. So, when deciding whether or not the mass is something related to breast cancer, the screening physicians must consider a differential diagnosis for a number of common ailments.

For relatively non-fatty masses: Cyst, fibroadenoma, solitary intraductal papilloma, dermal lesion, hematoma, abscess, phyllodes tumor, circumscribed malignancy.

For relatively ‘fatty’ masses: lymph node, cytosteatonecrosis (or fat necrosis), lipoma, hamartoma, galactocele.

Ultrasound differentiation of a benign versus malignant solid mass

A mass will be considered ‘malignant’ (until proven otherwise) when it contains any single malignant feature found on the ultrasound. These include angular margins, spiculations, shadowing, branch pattern extensions, certain microcalcifications, duct extensions, microlobulations, markedly hypoechoic, parietal thickening, intracystic nodules, size greater than 1 cm, and growth non-parallel to the skin.
The mass will be considered benign if it has no malignant features, plus few lobulations, an ellipsoid shape, intense uniform hyperechogenicity, and a thin echogenic capsule.
The mass will be called ‘indeterminate’ if there are no malignant feature and none of the benign combinations.
In the ultrasound image below, one notes a suspicious hypoechoic mass with microlobulations. This mass would definitely need to be biopsied, and would probably be given a BI-RADS classification of either category 4C, or 5. ( Many constituencies don’t use BI-RADS 4 a, b, and c, but simply differentiate between categories 4 and 5. If required to choose, this mass would most likely be considered a BI-RADS category 5 breast lesion.)
suspicious microlobulated hypoechoic mass ultrasound

BI-RADS categories of suspected masses: Probability of malignancy and usual follow up

The BI-RADS categories are based on various mass characteristics and indicate increasing probabilities of malignant breast cancer. These categories are described in more detail elsewhere, but biopsy is usually indicated at level 4. The chances of malignancy are greatly increased once features consistent with the ‘intermediate’ level of BI-RADS 4b are present, such as powderish microcalcifications along with microlobulated contours, and evolving asymmetric densities.

BI-RADS categoryScreening FindingsApproximate probability of malignancy Follow-up Recommendation
0Evaluation incomplete, needs additional imaging  
1Negative0mammogram at normal interval
2Benign0mammogram at normal interval
3Probably Benignless than 2%shortened interval mammogram
4Suspicious abnormalitiesRanges from 3 to 95%Consider a biopsy
4aSuspicious abnormalities3-10%biopsy
4bSuspicious abnormalities10-50%biopsy
4cSuspicious abnormalities50-95%biopsy
5Highly Suggestive of Malignancy95% or moreAppropriate confirmation and staging procedures
6Malignancy proven histologically100%Staging procedures and treatment therapies


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