Adenosis of the Breast

Adenosis is a non-cancerous condition that occurs when glands grow abnormally large. In adenosis of the breast, some of the lobules (milk-producing sacs) grow larger and contain more glands than usual.

Adenosis may cause a breast lump that you or your doctor can feel. It also may show up on a mammogram as an abnormal shape with small white calcium deposits. Since these features can also be signs of breast cancer, you’ll likely need to have a biopsy to rule out cancer. 

There are a few different subtypes of breast adenosis. All of them are non-cancerous. Adenosis that does not fit into any of the subtypes is called true adenosis, simple adenosis, or florid adenosis. 

Sclerosing adenosis

With sclerosing adenosis, enlarged lobules with an increased number of glands are accompanied by scar-like tissue. Sclerosing adenosis is found in over 1 in 4 benign breast biopsies. It develops most often during perimenopause.

Sometimes people with sclerosing adenosis have a rare second type of adenosis, too, called apocrine adenosis. It is similar to other types of adenosis but occurs in a specific type of gland cells called apocrine cells. 

Nodular adenosis

Nodular adenosis is a rare type of adenosis that results in a mass. It’s sometimes called an adenosis tumor. It's usually a type of sclerosing adenosis, but it can also grow more like other subtypes of adenosis. 

Microglandular adenosis

Microglandular adenosis is a very rare form of breast adenosis. Its structure is different from other types of adenosis. Microglandular adenosis can cause the same symptoms as other forms of adenosis, and it can make breast tissue feel more dense. It can but does not always become invasive carcinoma.

Most research on adenosis and breast cancer risk has been on sclerosing adenosis. Some studies suggest that sclerosing adenosis may increase the risk of breast cancer. For example, a Mayo Clinic study of more than 13,400 women with benign breast biopsies found that women who were diagnosed with sclerosing adenosis had about double the risk of developing breast cancer as women who didn’t have sclerosing adenosis. 

Some studies suggest that people who are already at risk of breast cancer who have sclerosing adenosis may be at even greater risk, but others have found conflicting results. In particular, it’s not clear if sclerosing adenosis increases breast cancer risk in people who have atypical hyperplasia, or the development of precancerous cells in the breast. On its own, atypical hyperplasia increases breast cancer risk by about four-fold. Having both atypical hyperplasia and sclerosis adenosis may increase breast cancer risk by 6.7 times, according to a 1989 landmark study of more than 10,300 women with a benign breast biopsy. The Mayo Clinic study, however, did not find that sclerosing adenosis changed the risk of breast cancer associated with atypical hyperplasia. So, it’s not clear if sclerosis adenosis changes breast cancer risk in people who already have atypical hyperplasia. 

Simple adenosis seems to be linked to only a slight increase in breast cancer risk — or maybe none at all.

One study from 1996 suggests that people aged 60 and older with atypical apocrine adenosis in addition to sclerosing adenosis — meaning the apocrine cells have a different structure than normal — have a higher risk of breast cancer, but there is not an increased risk for younger people. 

Microglandular adenosis can turn into both non-invasive (in situ) and invasive cancers. In about 1 in 4 cases, it becomes an invasive cancer. Doctors may be able to identify cases at high risk of becoming invasive cancer because they look different under a microscope. Because of the cancer risk, people with microglandular adenosis may need surgery to remove it.

In many cases, adenosis does not cause noticeable symptoms. Sometimes enlarged lobules that are close together may feel like a lump. And sclerosing adenosis may cause breast pain.

It’s unclear what causes adenosis, but researchers think the sex hormone estrogen may help trigger it by increasing the growth and division of estrogen receptor-positive breast cells.

Risk factors for adenosis include:

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  being overweight

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  starting your menstrual cycle before age 12

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  using hormonal birth control pills

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  using hormone replacement therapy (HRT)

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  having your first child after age 35 or never giving birth

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  not breastfeeding (if you have given birth)

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  family history of breast cancer

If you or your doctor notice adenosis because it forms a lump, you may need a mammogram. More often, a routine mammogram is what catches adenosis.

Both adenosis and breast cancer can show up as calcifications on a mammogram. Because the calcifications from both conditions can look similar, a biopsy is often needed to tell them apart. A specialist will look at the tissue removed during the biopsy under a microscope to diagnose adenosis. This is the only way to confirm the diagnosis and rule out breast cancer.

Adenosis usually doesn’t need to be treated unless it’s causing pain or other symptoms. Wearing a supportive bra can help reduce breast pain. In the rare cases that adenosis causes symptoms that cannot be managed, surgery is an option.