In women under 40 years of age, mammography is not recommended unless there is serious doubt. Breast tissue is mainly composed of adipose tissue and mammary gland structure. In mammography, adipose tissue is close to black in color, while the mammary gland structure is close to white. Since breast cancers originate from the mammary gland, they appear in white on mammography. Since the mammary gland structure is dominant in the breast in women under 40 years of age, a white breast tissue cannot be distinguished from a white breast cancer tissue. After the age of 40, the mammary gland structure in the breast tissue regresses and turns into adipose tissue. In this case, a white breast cancer tissue can be easily noticed in a black breast structure.