Complex sclerosing lesion

by Kimberly Wood, MD MSc FRCPC
March 4, 2022


What is a complex sclerosing lesion in the breast?

Complex sclerosing lesion (CSL) is a non-cancerous growth that develops when there is an increase in the number of glands and ducts surrounding an area of altered connective tissue called a scar in the breast. Although non-cancerous, CSL is associated with a small increased risk of developing breast cancer when compared to women without CSL.​ Another name for a CSL is a radial scar.

How do pathologists make the diagnosis of complex sclerosing lesion?

Complex sclerosing lesions (CSL) can be diagnosed after a small sample of tissue is removed in a procedure called a biopsy. The diagnosis can also be made after a larger area of tissue is removed in a procedure called a resection.

For many patients, a CSL is discovered incidentally after a biopsy or resection is performed for another reason. However, some CSL can be seen on screening mammography/ultrasound, especially when they are greater than 1 cm in size. Because a CSL can look very similar to breast cancer on mammography or ultrasound, a biopsy is performed to confirm the diagnosis.

What does a complex sclerosing lesion look like under the microscope?

When examined under the microscope, a CSL is made up of abnormal connective tissue that pathologists describe as fibrosis. The abnormal connective tissue is sometimes described as showing elastosis or elastotic because it contains numerous elastic fibers. Small irregularly shaped ducts and glands are often seen trapped within the area of fibrosis. Other non-cancerous changes that are often seen in the tissue surrounding a CSL include usual ductal hyperplasia (UDH), cysts, and apocrine metaplasia.

A+ A A-