Distinguishing Breast Cancer Tumors From Benign Masses

Several factors can help differentiate the two

woman pointing to a breast mass that's a breast cancer tumor
Lester Lefkowitz / Getty Images

Non-cancerous and cancerous breast lumps can be very different from each other when it comes to how they feel during a breast exam and what they look like in imaging tests. However, a number of benign breast changes mimic breast cancer, so it sometimes takes further testing to know for sure what's going on in your breast.

  Cancerous Non-Cancerous
Feel Firm, irregular margins, immobile Squishy, defined margins, mobile
Mammogram Spiky, fuzzy, or lumpy Uniform, round or oval
MRI Rapid light-up and fade Slow to light up, doesn't fade
Biopsy Cell clusters, irregular nuclei Same as normal cells

What It Feels Like

How a breast mass feels can give a doctor a fairly good idea whether a lump is a breast cancer tumor or a benign mass. In one study, palpation (feeling the lump) had an overall accuracy of around 90%.

Palpation of Cancerous Masses

Masses in the breast that are cancer are often very firm, like a rock or a carrot, and have an irregular shape and size. They are also often fixed—i.e., they feel like they are attached to the skin or nearby tissue so that you can't move them around by pushing on them—but can be mobile. They're also not likely to be painful, though they can be in some cases.

On exam, other changes may be present as well, such as dimpling of the skin or an orange-peel appearance, nipple retraction, or enlarged lymph nodes in the armpit.

One type of breast cancer, inflammatory breast cancer, does not usually cause a lump but instead involves redness, swelling, and sometimes a rash on the skin of the breast.

Palpation of Benign Breast Masses

In contrast to breast cancer tumors, benign lumps are often squishy or feel like a soft rubber ball with well-defined margins. They're often easy to move around (mobile) and may be tender.

Breast infections can cause redness and swelling. Sometimes it can be difficult to tell the difference between mastitis and inflammatory breast cancer, but mastitis often causes symptoms of fever, chills, and body aches, and those symptoms aren't associated with cancer.

Appearance on Mammogram

As with a physical examination, cancerous and benign masses may sometimes appear similar on a mammogram, but some findings are more common in one than the other.

It's important to note that around 20% of breast cancers do not show up on a screening mammogram. Similarly, benign breast conditions sometimes appear to be cancer.

Mass Due to Cancer

A breast cancer tumor on a mammogram is often irregular with edges that don't look smooth. A spiculated breast mass, which has spikes extending out from the main mass, is often highly suggestive of cancer. In fact, the word cancer is derived from the appearance of these crab-like extensions that invade nearby tissues. The edges of the mass may also appear fuzzy or indistinct.

When looking at mammogram pictures, cancers often appear bright and the area around the mass may be distorted. Breast calcifications, especially calcifications in clusters, may be visible as well.

Mass Due to Benign Conditions

On a mammogram, benign tumors often appear round or oval (ellipsoid) with clear, well-defined edges.

Exceptions

Benign conditions such as breast adenosis, fat necrosis, and radial scars may look very similar to cancers on a mammogram, with spiky masses or microcalcifications.

Appearance on Ultrasound

A breast ultrasound is a helpful test to distinguish between solid and cystic masses. In looking at an ultrasound report, the term hypoechoic refers to an area on the study that appears darker, and it means the area is solid.

Mass Due to Cancer

On ultrasound, a breast cancer tumor is often seen as hypoechoic, has irregular borders, and may appear spiculated. Other ultrasound findings that suggest breast cancer include:

  • Non-parallel orientation (not parallel to the skin)
  • A mass that is taller than it is wide
  • Acoustic shadowing (a finding that indicates a solid mass)
  • Microlobulation (collections of small lobes on the surface of a solid mass)
  • Duct extension
  • A branching pattern
  • A mass within a cyst
  • Angular margins (an irregular or jagged appearance)

Mass Due to Benign Conditions

With benign masses, a fluid-filled cyst may be noted. Solid areas usually:

  • Are uniform
  • Are oval
  • Have a clearly defined capsule
  • Are parallel to the skin
  • Have three or fewer lobulations

MRI Appearance

A breast magnetic resonance imaging (MRI) scan can sometimes provide better distinction than a mammogram when it comes to masses due to cancer and those related to benign causes. That's especially true in women who have dense breasts.

During a breast MRI, a contrast agent is injected into the bloodstream. When this contrast "lights up" a region on the image, the region is said to be enhanced.

Malignant Breast Tumor

Cancerous masses on MRI differ both in general appearance and the length of time they appear (kinetics). A cancerous mass often has irregular or spiculated borders with internal divisions that becomes enhanced. Rim enhancement (brightening) on the outside of the mass is also common.

Cancerous tumors also often have what's called rapid signal intensity, which means they light up rapidly from the contrast when the image is taken, but then wash out (dim) rapidly.

Benign Breast Tumor

On MRI, benign breast masses often have smooth borders or are lobulated. If there's enhancement, it's usually minimal or patchy. The rise in signal intensity is slow (the image becomes bright only very slowly) and it doesn't wash out.

Biopsy Appearance

When a breast biopsy is done, the tissue is sent to a pathologist to look at under a microscope (special molecular studies are usually done as well). The pathologist looks at the size and shape of the cells, as well as their arrangement if the sample was retrieved via a core or open biopsy.

Breast Cancer Tumor Cells

Under the microscope, breast cancer cells may appear similar to normal breast cells (well-differentiated) or very little like breast cancer cells (poorly differentiated), depending on the tumor grade. Cancer cells differ from normal cells in many ways.

The cells may be arranged in clusters, and they may be seen invading blood vessels or lymphatic vessels. The nucleus of cancer cells can be striking, with nuclei that are larger, irregular in shape, and stain darker with special dyes. There are also often extra nuclei, rather than just one.

Benign Breast Mass Cells

Benign breast cells may or may not look identical to normal breast cells, depending on the type of mass, but they don't look like cancer cells.

A Word From Verywell

Learning about all of these differences between breast cancer tumors and benign breast masses really helps illustrate why all of these tests are done. Likewise, knowing about the limitations and exceptions to all of these "general rules" helps explain why a doctor may sometimes recommend a breast biopsy even if other findings strongly suggest that a mass is either benign or malignant.

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