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.
The adult breast is composed of small structures called glands that are arranged into groups called lobules. The main function of these lobules is to produce milk. The milk travels from the lobules to the nipple through small tubes called ducts. The lobules and ducts are lined by specialized cells called epithelial cells.
Complex sclerosing lesions 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.
When examined under the microscope, the ducts in a CSL have more epithelial cells than normal ducts which pathologists describe as usual ductal hyperplasia. There are also large ducts called cysts. Pathologists call the combination of an increased number of epithelial cells and cysts proliferative change.