Dense Breast Tissue

The breasts are composed of tissue made up of lobules that produce milk, ducts that transport the milk to the nipple, and supporting tissue such as fatty tissue and fibrous connective tissue. The lobules and milk ducts form the structure of the breast and are responsible for milk production. Fatty and fibrous tissues give shape to the breast. The combination of fat and fibrous tissue is referred to as the "glandular" structure.

This condition is entirely genetic. Functionally, there is no difference between dense breast tissue and lipoma (fatty tissue-dominant) breast tissue in terms of milk production. This is not an abnormal condition, but rather a common structural feature.

Dense breast tissue is more commonly seen in younger women and those with smaller breast structures. However, it can occur in all age groups and with all breast types. As age progresses, the density of the breast decreases.

In dense breasts, malignant tumors can sometimes go unnoticed. This is because the different structures that make up the breast tissue each allow X-rays (mammography) to pass through to varying degrees. Fatty tissue has low resistance, allowing most of the X-rays to pass through, which causes these areas to appear black on the mammogram. Glandular and fibrous tissues are relatively more resistant, meaning that some of the X-rays are blocked, causing these tissues to appear gray/white. Cancerous tissue is also dense and allows very little X-ray penetration, making it appear gray/white as well. The main reason tumors may go unnoticed in dense breasts is due to this characteristic.

The presence of dense breast tissue indicates a moderate increase in risk. A screening program will be tailored by the radiologist, taking into account other risk factors. Depending on breast density, mammography screening may continue, or additional imaging such as breast ultrasound or breast MRI may be performed.

Dense breast tissue does not create a high risk when considering other factors such as age, early menstruation/late menopause, a family history of breast cancer, or BRCA gene mutations.

General Features of Dense Breasts

• Dense breasts can lead to misinterpretations on mammography.
• The frequency of dense breasts decreases after menopause.
• Breast ultrasound is preferred either in addition to mammography or directly.
• The risk of cancer is 4-6 times higher compared to breasts with normal density.
• While mammography has a 98% success rate in detecting cancer in normal breast tissue, this rate drops to 48% in dense breasts.
• The likelihood of cancer recurrence is higher in dense breasts.
• Breast density is a characteristic that can only be assessed through mammography. It cannot be determined through physical examination or ultrasound. Radiologists use two BIRADS (Breast Imaging Reporting and Data System) scales, and the ACR (American College of Radiology) BIRADS scale defines breast density as follows:
• Type 1 = Fatty Tissue: The breast is almost entirely composed of fatty tissue. Mammography results are sensitive enough to detect even the smallest tumors.
• Type 2 = Scattered Fibroglandular (gland-like) Tissue: A mix of fatty tissue with some glandular and fibrous tissue. There is a minor decrease in sensitivity.
• Type 3 = Heterogeneously Dense Tissue: More glandular and fibrous tissue, making small lesions harder to detect. Results are moderately sensitive.
• Type 4 = Extremely Dense Tissue: Almost all of the breast is made up of glandular and fibrous tissue, making it easy for tumors to go unnoticed. Results are of low sensitivity.

Another BIRADS scale categorizes mammography results. Reports typically consider this scale:

0 = Additional imaging needed for comparison.

1 = Negative.

2 = Appears benign.

3 = Likely benign; short-term follow-up is recommended.

4 = Suspicion of abnormal cells; biopsy is recommended.

5 = High likelihood of malignancy.

6 = Proven malignant tumor.