A breast hematoma is a collection of blood that pools inside the breast tissue, forming a lump. It is not cancer. Hematomas develop when blood vessels in or around the breast break and leak blood into the surrounding tissue, where it collects into a contained pocket. The result feels like a lump that can be spongy or firm to the touch, often with visible bruising on the skin above it.
What Causes a Breast Hematoma
The most common cause is some form of trauma to the breast. That includes surgical procedures like biopsies, lumpectomies, breast augmentation, or reduction surgery. Any time a needle or scalpel passes through breast tissue, small blood vessels can be damaged, and blood can accumulate in the area afterward. Post-surgical hematomas are one of the more frequent complications of breast procedures.
Blunt force injuries, such as a seatbelt injury in a car accident, a fall, or a sports impact, can also cause a hematoma. In rarer cases, a breast hematoma develops spontaneously in people taking blood-thinning medications. Anticoagulants interfere with the body’s clotting process, which means even minor, unnoticed vessel damage can lead to significant blood accumulation. Spontaneous breast hematomas without trauma or blood thinners are uncommon.
How It Looks and Feels
The symptoms depend on how deep the blood collects. A hematoma near the surface of the breast typically produces visible bruising right away, along with swelling and tenderness. A deeper hematoma may not show any skin discoloration for several days, and the first thing you notice could be a new lump or an area of firmness in the breast.
As the hematoma ages, the bruise on the skin shifts through a predictable color cycle: dark purple or red at first, then green, gray, and finally yellow before fading entirely. Pain and tenderness usually peak in the first few days and gradually ease. Some hematomas are painless from the start, particularly smaller ones that form deep in the tissue. The lump itself can range from soft and spongy (when the blood is still liquid) to quite firm (once the blood starts clotting).
Why Imaging Is Important
A breast hematoma can look and feel remarkably similar to a tumor. On a physical exam alone, it is sometimes impossible to tell the difference, which is why imaging is a standard part of the evaluation. Ultrasound is usually the first step. A fresh hematoma typically appears as a cystic (fluid-filled) area, sometimes with thin internal lines of fibrin (clotting material) or a layered appearance where clotted blood settles toward the bottom.
On mammogram, a hematoma can show up as a dense mass. In some cases, particularly when the hematoma is older and has developed irregular borders from scarring, it can closely mimic the appearance of breast cancer. One published case in Cureus described a breast hematoma that was initially read as “very concerning for malignancy” on CT and scored as highly suspicious on ultrasound, only to be confirmed as a hematoma on biopsy. This kind of false alarm is not unusual.
Certain features on imaging help radiologists lean toward a benign diagnosis. Fat content visible on mammography or MRI suggests a post-traumatic process rather than cancer. The absence of blood flow within the mass on ultrasound is also reassuring, since cancerous masses tend to develop their own blood supply. On the other hand, if the mass contains a solid, vascularized (blood-supplied) component, that raises suspicion and typically leads to a biopsy. Any hemorrhagic breast mass that appears without an obvious trigger like recent surgery or known trauma warrants further investigation.
Hematoma vs. Cancer
A breast hematoma does not increase your risk of developing breast cancer. The two are unrelated conditions. The concern is not that a hematoma will become cancer, but that a hematoma can mask cancer on imaging, or that what appears to be a hematoma could actually be a bleeding tumor. Certain cystic breast cancers, including some papillary carcinomas, can contain blood products and initially look similar to a hematoma on ultrasound or mammogram.
This is why follow-up matters. If you have a known hematoma, your doctor will likely recommend repeat imaging after several weeks to confirm it is shrinking. If a hematoma does not resolve completely, or if a residual mass or abnormality persists on mammogram, a biopsy is recommended to rule out an underlying malignancy.
How Breast Hematomas Are Treated
Most breast hematomas resolve on their own. The body gradually breaks down and reabsorbs the pooled blood over a period of weeks. During that time, the bruising fades, the swelling decreases, and the lump softens and shrinks. Cold compresses in the first 24 to 48 hours can help limit further swelling, and over-the-counter pain relief can manage discomfort.
Larger hematomas, or those that cause significant pain and pressure, may need to be drained. This can be done with a needle (aspiration) if the blood is still liquid, or it may require a small surgical procedure if the blood has clotted into a solid mass. If you are on blood-thinning medication, your doctor may temporarily adjust your dosage to allow the area to heal, though that decision depends on why you are taking the medication in the first place.
What Happens as a Hematoma Heals
As the body reabsorbs the blood, you may feel the lump change texture over time. It often starts out relatively soft and becomes firmer as the blood clots, then gradually softens again as the clot breaks down. The bruise follows its color progression from dark to yellow, and tenderness fades along with it.
In some cases, a hematoma does not fully reabsorb. Instead, the body walls it off with scar tissue, and the fat cells in the area can die, creating a condition called fat necrosis. Breast tissue is particularly rich in fat, which makes it relatively prone to this outcome after trauma. Fat necrosis produces oil cysts (small pockets of liquefied fat), calcifications, or areas of firmness that can persist long after the original injury. These are benign, but they can show up on future mammograms as suspicious-looking findings, including spiculated masses or unusual calcifications. Radiologists familiar with your history can usually interpret these correctly, but in some cases a biopsy is still needed to be sure. Research published in the British Journal of Radiology notes that follow-up at two years allowed doctors to track how hematomas evolved into scars or fat necrosis over time.
If you have had a breast hematoma, mention it during future mammogram appointments. Knowing about prior trauma helps the radiologist interpret any lingering changes in the tissue and avoid unnecessary alarm.