Sclerosing adenosis is a noncancerous (benign) change in the breast made up of an increased number of small glands that are surrounded and squeezed by dense, scar-like connective tissue. The name describes exactly what the pathologist sees: “adenosis” means more glands than usual, and “sclerosing” means the scar-like tissue that compresses them.
Sclerosing adenosis is common and is often found as part of fibrocystic change, a group of benign changes that occur together in the breast. It cannot spread to other parts of the body. It matters for two reasons: it can look like breast cancer both on imaging and under the microscope, and it is associated with a small increase in future breast cancer risk.
This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.
Sclerosing adenosis rarely causes symptoms and usually cannot be felt as a distinct lump. It is most often found on a mammogram, where it may appear as a density or as a cluster of small calcium deposits called microcalcifications. Because these findings can resemble breast cancer on imaging, a biopsy is usually performed to determine what is causing them.
The exact cause of sclerosing adenosis is not known. It is believed to develop as part of the normal breast’s long-term response to hormones, which is why it commonly occurs alongside the other changes grouped under fibrocystic change. It is not caused by injury or surgery, despite the scar-like appearance of the tissue.
The diagnosis of sclerosing adenosis is made after breast tissue is examined under the microscope by a pathologist. The tissue usually comes from a core needle biopsy performed to investigate an abnormal area on a mammogram. Sclerosing adenosis is also commonly an incidental finding in tissue removed for another reason. Under the microscope, it is made up of crowded, small glands arranged in a rounded group that keeps the outline of a normal lobule. The glands are compressed and distorted by dense connective tissue called collagen, and microcalcifications are commonly seen within the glands and the surrounding tissue.
Because the glands are crowded and distorted, sclerosing adenosis can closely resemble invasive ductal carcinoma under the microscope. Two features separate them. The first is the overall shape: sclerosing adenosis keeps the rounded, organized outline of a lobule, while invasive cancer grows in a disorganized way through the surrounding tissue. The second is the presence of myoepithelial cells, a supporting layer of cells that surrounds normal glands and is preserved in sclerosing adenosis but lost in invasive cancer. When the distinction is difficult, the pathologist performs immunohistochemistry (IHC) to highlight the myoepithelial cells and confirm that the change is benign.
Sclerosing adenosis is classified as a proliferative change without atypia, meaning there is an increase in the number of normal-looking cells but no abnormal-looking (atypical) cells. Changes in this category are associated with a modest increase in the lifetime risk of developing breast cancer, roughly 1.5 to 2 times that of a person without the condition. The overall risk remains low, and most people with sclerosing adenosis never develop breast cancer. Your personal risk also depends on other factors, including family history and whether any atypical changes were found in the same sample.
Sclerosing adenosis is benign and usually requires no treatment once the diagnosis is confirmed. The pathology findings, together with your imaging, guide what your team recommends next.