As women age, breast tissue composition changes. The composition of breast tissue can greatly affect the results of a mammography screening. In young women breasts are composed of firm glandular tissue, which appears denser. In mammography, this density appears as a thick, white area. Cancerous tumors also appear as densities on a mammogram. This can make it difficult to distinguish between the two.

As women age, most breast density decreases and tissue becomes fattier. Fatty tissue appears dark on a mammogram, making it easier to see the white areas of potential tumors. Breast density is directly related to the level of estrogen in the body. During menopause, estrogen levels drop causing breast tissue to shrink and more fatty tissue to develop. Hormone replacement therapy (HRT) replaces lost estrogen. For women on HRT, breast tissue remains dense and therefore difficult to evaluate. (This is a concern due to the fact that HRT occurs at an age when women's risk of breast cancer is significantly higher).

When young women find lumps in their breasts, they are usually benign cysts, or clumps of normal glandular tissue. However, any solid lump that gets bigger is often further evaluated to make sure it is not cancer. Common methods for evaluation start with additional imaging techniques and proceed to biopsy if it is necessary.

As part of your mammogram report, the radiologist may use a special code known as the Breast Imaging Reporting and Data System, or BIRADS.

0	More information is needed to give a final mammogram report.
1	Your mammogram is normal.
2	Your mammogram shows only minor abnormalities that are not suspicious for cancer. No additional testing is needed.
3	Your mammogram shows minor abnormalities that are probably benign. The radiologist may recommend follow-up testing in six months to make sure the suspicious area has not changed.
4	Your mammogram shows a suspicious change, and a biopsy should probably be performed. However, less than half of women with category 4 mammograms will end up having cancer.
5	Your mammogram shows a worrisome change. A biopsy is strongly recommended. Up to 80 percent of women with a category 5 mammogram will end up having cancer.