Final answer:
Extremely dense breasts have significantly more epithelial cells in TDLUs, leading to an increased risk of breast cancer. Mammograms can identify dense regions which may indicate cancer, but diagnosis is more challenging in denser breasts due to lower contrast in X-ray absorption.
Step-by-step explanation:
The breast consists of mammary glands and fat tissue, with the size of the breast largely determined by the amount of fat present. Breasts with a higher density have a more significant concentration of epithelial cells in the terminal ductal lobular units (TDLUs), which are integral to milk production and secretion. Studies suggest that women with extremely dense breasts have a 1.8 to 6 times increased risk of breast cancer as compared to those with fatty breasts.
This could be attributed to the high number of epithelial cells, where cancer often originates. While mammograms are a critical tool for early detection, it's important to note that they do not diagnose cancer but instead provide evidence of dense regions which might signal a tumor's presence. For younger women with denser breasts, differential X-ray absorption is challenging, making diagnosis more difficult. In contrast, the presence of more fat in older women's breasts, who are generally at higher risk for breast cancer, allows for better tumor contrast during such diagnostics.