Mammograms are specialized X-ray images of the breast, serving as a primary tool for detecting changes within breast tissue. Their main role is the early identification of breast cancer, often before noticeable symptoms appear. Early detection can lead to improved treatment outcomes.
How Mammograms Work to Identify Abnormalities
Mammograms use low-dose X-rays to create detailed images of the breast. During the procedure, the breast is gently compressed by a paddle. This compression helps spread breast tissue, minimize movement, and allow for a clearer image with less radiation.
X-rays pass through the breast tissue to a detector, forming a digital image. Different types of breast tissue, such as fat, glandular tissue, and potential tumors, absorb X-rays differently. Fatty tissue appears darker or more translucent on a mammogram, while denser tissues like glandular tissue, connective tissue, and tumors appear whiter.
Modern mammography often utilizes digital breast tomosynthesis, also known as 3D mammography. While 2D mammograms provide a single flat image, 3D mammography captures multiple low-dose images from various angles. A computer then reconstructs these images into thin “slices,” allowing radiologists to view breast tissue layer by layer. This multi-layered approach can enhance the visibility of abnormalities, particularly in individuals with dense breast tissue, and may reduce the need for follow-up imaging.
Common Appearances of Breast Cancer on Mammograms
Radiologists examine mammograms for specific visual indicators of breast cancer, including masses, calcifications, architectural distortion, and asymmetry. Each characteristic has distinct features that help assess its potential nature.
Masses
Masses appear as lumps within the breast tissue. Their shape, margin, and density provide clues about their likelihood of being cancerous. Masses with irregular shapes and indistinct or spiculated (spiky or star-shaped) margins are generally more concerning. Conversely, round or oval masses with well-defined, circumscribed margins are often benign, such as cysts or fibroadenomas.
Calcifications
Calcifications are tiny calcium deposits that appear as small white spots. Most are not associated with cancer, but certain patterns can be suspicious. Suspicious calcifications are often small, irregular in size or shape, and tightly clustered. Examples include fine pleomorphic calcifications (variable shapes) and fine linear or branching calcifications, which suggest deposits within a duct.
Architectural Distortion
Architectural distortion refers to a disruption of the normal breast tissue pattern without a distinct mass. It appears as if the tissue is being pulled or retracted, often with thread-like projections. This finding can be subtle but can be a sign of breast cancer.
Asymmetry
Asymmetry describes an area of increased density in one breast compared to the corresponding area in the opposite breast, or a change from prior mammograms. While many asymmetries are benign, a “developing asymmetry” – an area that is new or more noticeable than on previous exams – can be a concerning finding and often requires further evaluation. When asymmetry is accompanied by architectural distortion, calcifications, or an underlying mass, the probability of malignancy increases.
Differentiating Benign from Suspicious Findings
Radiologists analyze the characteristics of masses, calcifications, architectural distortions, and asymmetries, along with a patient’s clinical history, to determine the likelihood of a finding being cancerous. Not all abnormalities seen on a mammogram indicate cancer; for example, simple cysts are benign fluid-filled sacs that typically do not require biopsy.
To standardize the interpretation and reporting of mammogram findings, radiologists use the Breast Imaging Reporting and Data System (BI-RADS). This system assigns a category from 0 to 6 to each finding, indicating the level of suspicion and recommending next steps.
BI-RADS 0: Assessment incomplete, requiring additional imaging or comparison with previous studies.
BI-RADS 1: Negative or normal finding, suggesting routine screening can continue.
BI-RADS 2: Benign finding with no probability of malignancy.
BI-RADS 3: Probably benign, with a very low probability of malignancy (less than 2%), often warranting short-interval follow-up.
BI-RADS 4: Suspicious finding, with a probability of malignancy ranging from 2% to 95%, usually suggesting considering a biopsy. This category is further divided into 4A (low suspicion), 4B (moderate suspicion), and 4C (high suspicion).
BI-RADS 5: Highly suggestive of malignancy (over 95% probability), strongly recommending biopsy.
Next Steps After a Suspicious Mammogram
When a mammogram reveals a suspicious finding, further evaluation is typically recommended. Most abnormal findings do not turn out to be cancer. The initial step often involves additional imaging.
Diagnostic Mammogram
A diagnostic mammogram takes more focused images of the area of concern, sometimes with special views or magnification. This allows the radiologist to get a clearer picture of the abnormality’s shape, margins, and density.
Breast Ultrasound
Breast ultrasound uses sound waves to create images. It is particularly useful for distinguishing between solid masses and fluid-filled cysts, which appear differently on ultrasound. This can help determine if a mass is benign or requires further investigation.
Breast MRI
In some cases, a breast Magnetic Resonance Imaging (MRI) may be recommended. MRI uses magnetic fields and radio waves to generate detailed images of breast tissue. It is often used for high-risk individuals or when other imaging results are inconclusive.
Biopsy
If imaging tests continue to show a suspicious area, a breast biopsy is typically the next step. A biopsy involves removing a small sample of tissue from the suspicious area for examination under a microscope by a pathologist. This is the definitive method for diagnosing whether a finding is cancerous. Common types include fine needle aspiration (FNA), core needle biopsy, stereotactic biopsy, and ultrasound-guided biopsy, which use imaging to precisely guide the needle. If the biopsy confirms cancer, appropriate treatment can then be planned.