Mass shape, margin, and density as found with screening mammography

When a mammogram is interpreted by a radiologist, there are a number of characteristic abnormalities in breast tissue which they will be looking for. Sometimes they will note simple changes in density,a 'distortion', or the presence of microcalcifications, but at others times the breast X-ray will clearly reveal a 'mass', which may not be clinically palpable. Most breast masses occur due to benign causes, but certain characteristics of mass may be more suspcisious for breast cancer.


x-ray of a breast mass


When is a 'lesion' called a 'mass' ?

A mass is usually something a little more substantial and clear than a 'lesion' per se. A mass has volume; it occupies space. It may be in any shape but usually with convex outside borders. It tends to be denser in the middle than towards the edges. A mass will not be interspersed with fat cells to the same degree as non-affected tissue. A mass found during a mammogram will typically be described according to it's shape, density ( the amount of fat cells present and density of suspicious cells), and its margin (characteristics of it's 'edge').

Summary of typical mass characteristics

Shape Likely Benign Suspicious Highly Suspicious of Malignancy
Round X    
Oval X    
Lobular X X  
Irregular     X

If the mass appears more like a 'lobule' than a purely round or oval shape, then it is somewhat more suspicious for breast cancer. Masses appearing with a very irregular, or 'random' shape or highly suspicious for breast cancer.

Breast mass density is expressed according to the relative amount of fat tissue present

Density Likely Benign Suspicious Highly Suspicious of Malignancy
Quite fatty X    
Low X    
Iso X X  
High     X


The 'density' of a mass, in terms of the relative amounts of fatty elements present, becomes highly suspcious for breast cancer when the density is high. In other words, when there is little mammographic evidence of fatty tissue within the mass, this tends to suggest that the mass is composed primarily of malignant cancer cells.

The margin of the breast mass is suspicious for breast cancer when it is ill-defined or spiculated

Margin Likely Benign Suspicious Highly Suspicious of Malignancy
Well-defined X    
Obscured/75% hidden or more   X  
Microlubulated   X  
Indistinct and ill-defined   X X
Spiculated     X

A radiologist interpreting a breast cancer screening mammogram will be alarmed when they discover a mass with an poorly defined or spiculated margin. Or, if the margin seems 'blurry', that might indicate that breast cancer cells are infiltrating into the surrounding tissue. Most benign breast lesions and tumors have well-defined borders, but not all. A mass with an ill-defined margin will certainly be re-evaluated using ultrasound (ultrasound is quite good for determining the nature of mass borders), and sent for biopsy if there is still concern.

Remember that mass is but one of many diagnostic characteristics with breast cancer. Other techniques and attributes are then used to predict the potential malignancy of the lesion and the extent to which it may have spread.



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