Your pathology report for complex sclerosing lesion of the breast

by Kimberly Wood, MD MSc FRCPC
October 3, 2025

A complex sclerosing lesion (CSL) is a benign (noncancerous) growth in the breast. Under the microscope, it has a central area of scar-like tissue with ducts and glands radiating outward, which is why it is sometimes referred to as a radial scar.

Although the name includes the word “scar,” CSLs do not develop after injury or surgery. They are abnormal growths of breast tissue that mimic the appearance of scar tissue.

CSLs themselves are not cancerous, but women with CSLs have a slightly higher risk of developing breast cancer compared to women without CSLs.

What are the symptoms of a complex sclerosing lesion?

Most CSLs do not cause symptoms. They are often found by chance when breast imaging (such as mammography or ultrasound) is performed for another reason. Rarely, a CSL grows large enough to be felt as a lump in the breast.

What causes a complex sclerosing lesion?

Doctors do not yet know what causes CSLs to develop. They are thought to arise from an overgrowth of normal breast tissue components, particularly the ducts, glands, and supporting connective tissue.

Is a complex sclerosing lesion linked to breast cancer?

CSLs are not cancer, but studies have shown that women with CSLs have a slightly higher risk of developing breast cancer compared to women without CSLs.

This increased risk may be related to additional changes that are sometimes seen in and around CSLs, such as:

  • Proliferative changes – An increase in the number of normal cells in the ducts and glands.

  • Atypia – Cells that look abnormal but are not cancer.

Because CSLs can sometimes hide or occur next to cancer, doctors often recommend surgical removal or careful follow-up to ensure no cancer is present.

How is this diagnosis made?

CSLs may first be suspected on imaging studies such as mammography or ultrasound, especially if the lesion is larger than 1 cm. They can look very similar to breast cancer on imaging, which is why a biopsy is usually needed.

  • Biopsy – A small piece of tissue is removed with a needle. If the pathologist sees features of CSL, the diagnosis can be made.

  • Surgical excision – Sometimes the entire lesion is removed, especially if the biopsy shows atypia or if imaging raises concern for cancer.

Many CSLs are found incidentally when tissue is removed for another reason.

Microscopic features

When examined under the microscope, a CSL often shows the following features:

  • Fibrosis – Scar-like connective tissue in the center of the lesion.

  • Elastosis – Connective tissue rich in elastic fibers, giving the scar-like area a dense appearance.

  • Trapped ducts and glands – Small, irregular ducts and glands pulled into the fibrous tissue, giving the radial (spoke-like) pattern.

Other benign changes often seen around a CSL include:

These changes are noncancerous and do not, on their own, increase the risk of cancer.

Questions to ask your doctor

  • Was the lesion in my breast diagnosed as a complex sclerosing lesion or radial scar?

  • Did the biopsy show any atypia or other changes?

  • Do you recommend surgical removal, or can this be safely monitored with imaging?

  • Does this lesion increase my risk of breast cancer?

  • How often should I have follow-up mammograms or other screening?

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