Pseudoangiomatous Stromal Hyperplasia (PASH)

There are several benign breast conditions that aren’t breast cancer. One of these is pseudoangiomatous stromal hyperplasia (PASH).

PASH is usually found incidentally during breast imaging. While it can sometimes cause a painful lump that needs to be removed, it isn’t dangerous and doesn’t increase the risk of breast cancer.

A PASH growth is usually rubbery, pale, round or oval-shaped, and has well-defined edges. It’s made up of slit-like spaces lined by long cells called spindle cells. The spindle cells make what may look like — but aren’t — blood vessels. Inside the slit-like spaces is collagen, a protein that acts as a building block for tissue. This collagen is what can make a PASH lump grow quickly.

​​PASH has been found in about 23% of breast biopsy samples done for other reasons. It’s most common in premenopausal and perimenopausal women in their 30s to 50s, as well as postmenopausal women taking hormone replacement therapy. But PASH has also been found in people aged 14 to 86, and in about 24% to 47% of men with gynecomastia — a growth of breast tissue.

There is no evidence that PASH increases breast cancer risk. “It's not something that's ever going to become cancer,” says Wendie Berg, a radiologist at the University of Pittsburgh Medical Center’s Hillman Cancer Center. “It's not a risk factor for developing cancer.”

One large study found that women with PASH actually had a lower risk of breast cancer, but this link hasn’t been confirmed.

In rare cases, PASH may be mistaken for a similar-looking breast growth called angiosarcoma. The difference is that angiosarcoma has spaces filled with blood vessels, whereas PASH doesn’t. 

It’s important to tell the two apart because angiosarcoma is a cancer of the blood and lymph vessel lining. The treatment needed for PASH and angiosarcoma is different.

In instances where it’s difficult to tell whether a person has PASH or angiosarcoma, immunohistochemistry can help. It uses antibodies to detect specific antigens in the tissue, and the two conditions have different antigens. “It’s easy to do those tests if they’re at all concerned,” Berg says.

In many cases, PASH doesn’t cause any symptoms. That’s why it’s often found in breast imaging tests — like mammograms, ultrasound, or MRI — that aren’t looking for PASH.

When PASH does cause symptoms, they may include:

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  breast growth

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  breast lump

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  tender or painful breast

Experts aren’t sure what causes PASH. It seems to be related to changes in hormone levels, especially of the hormone progesterone. Sometimes estrogen may also make PASH grow.

Sometimes people go to the doctor because they found a breast lump, and it turns out to be PASH. Other times, they have breast imaging for another reason, and PASH shows up.

Because doctors can’t be sure a growth is PASH based on imaging, they do a core needle biopsy to diagnose it.  During a core needle biopsy, a healthcare provider sticks a hollow needle — about 2 millimeters across — into the breast growth and removes small amounts of tissue. The procedure only takes about 15 to 20 minutes. People are given a local anesthetic beforehand, so it usually doesn’t hurt, but it can be painful for some people. Afterward, a specialist looks at the breast tissue under a microscope to diagnose what type of growth it is.

If PASH isn’t causing symptoms and doesn’t grow too large, you can take a wait-and-see approach to treatment. If you choose this option, your doctor will check the area every six months.

People nearing menopause may choose this approach because PASH often shrinks afterward, as long as they aren’t taking hormone replacement therapy, says Berg.

But if the lump becomes painful, develops quickly, or grows above 2 or 3 cm, you’ll probably need surgery to remove it. “If it grows quickly and becomes a large lump that one can feel, it's likely to continue to get bigger,” Berg says.

Usually, just the lump is removed. In rare cases where the lump is very big, a mastectomy may be done.

PASH grows back in 15% to 22% of people who have surgery to remove it. This might happen if only part of the growth was removed during the procedure, or it may simply recur. 

In very rare cases, anti-estrogen therapy may be used to help shrink PASH. This can mean taking tamoxifen, a medicine also used to treat hormone receptor-positive breast cancer that may cause side effects. But surgery is a much more common treatment.

Although a PASH diagnosis can be unsettling, it’s a benign condition that often requires little or no treatment. With appropriate follow-up, most people with PASH do well. “It's nothing to worry about,” Berg says.