Before we delve into breast disease, let's refresh our memory of how a benign duct and acinus look. These are the two components that make up the terminal duct lobular unit (TDLU). For a more in-depth review of breast histology, go read my "Breast basics" post.
Commonly encountered benign breast diseases include fibrocystic changes, fibroadenomas/phyllodes tumors, inflammation/mastitis, intraductal papillomas and fat necrosis. We will go into more details of each of these entities in separate posts.
Benign breast diseases can be broken down into three major categories:
1. Non-proliferative lesions
2. Proliferative lesions
3. Proliferative lesions WITH atypia
Non-proliferative breast lesions do NOT have an increased risk of developing breast cancer. Their lifetime risk is the same as the general population (~3%). There may be mild hyperplasia present, but these changes in the breast are very benign and often due to the aging process, inflammation or chronic irritation. Beware though- apocrine and squamous metaplasia can look pretty ugly sometimes!
In contrast to NON-proliferative lesions, those classified as proliferative breast disease (containing an increased number of epithelial cells) are 1.5 to 2 times INCREASED RISK FOR BREAST CANCER (7% overall)!
Atypical ductal or lobular hyperplasia carry a significantly higher risk for developing breast cancer. They are four to five times more likely to develop cancer compared to the general population; approximately 17% lifetime risk! These lesions will be discussed in greater detail in the upcoming sections on ductal and lobular proliferative breast disease.