When a group of cells display uninhibited growth, which refers to division beyond the normal limits, this phenomenon is commonly referred to as cancer. Other characteristics include an attack and destruction of surrounding tissues, and the spread to other locations in the body via lymph or blood, which is known as metastasis.

These malignant, which refers to a severe and progressively worsening disease, properties of cancers differentiate them from benign tumors, which are self-limited and do not invade or metastasise.

A tumor refers to a swelling or lesion formed by an unusually high growth of cells and occurs with most cancers. However, some, like leukemia, do not produce tumors.

Breast cancer becomes established, initially, in the cells of the breast in men and women. On a worldwide basis, the second most established form of cancer, after lung cancer, is that of breast cancer. It represents 10% of all cancers relating to both sexes. It is the fifth most common cause of cancer death.

The most common type of cancer specifically related to women, globally, is that of breast cancer. It occurs at more than twice the rate of that of colorectal cancer and cervical cancer and about three times that of lung cancer. Further, in the case of women, deaths from breast cancer, worldwide, is approximately 25% more than that from lung cancer.

In a study in 2005, it was found that breast cancer produced 502,000 deaths worldwide. To get this into context, this represents about 7% of all cancer deaths, and nearly 1% of all recorded deaths. Further, there has been a substantial increase, globally, in breast cancer since the 1970s. This statistic, it is suggested, may be associated with modern lifestyles in the western world.

On a global basis, the occurrence of breast cancer differs significantly according to region. It is less widespread in less-developed countries and more so in the further-developed countries. In the twelve designated regions of the world, the annual incidence rates per 100,000 women are as follows: Eastern Asia, 18; Southern Central Asia, 22; sub-Saharan Africa, 22; South-Eastern Asia, 26; North Africa and Western Asia, 28; South and Central America, 42; Eastern Europe, 49; Southern Europe, 56; Northern Europe, 73; Oceania, 74; Western Europe, 78; and in North America, 90.

The United States has the highest incidence rates of breast cancer in women, globally. A study has shown 141 cases among white women and 122 among African American women. Also in the US, breast cancer amongst women is the most prevalent cancer. After lung cancer, it produces the second highest occurrence of deaths from all cancers.

There is a 12.5% chance of women in the US developing invasive breast cancer within their lifetime. Further, there is a 3% chance that the breast cancer that they may contract will actually cause their death. A forecast has suggested that, in 2007, breast cancer would be the cause of 40,910 deaths in the US. This would represent some 7% of cancer deaths, and almost 2% of all deaths.

For the last few years, both the incidence and death rates from breast cancer in the US have been in decline. In 2005, a study conducted in the US by the Society for Women's Health Research concluded that breast cancer remains the disease that causes the most concern. This is an interesting outcome since heart disease is a much more widespread determinant when considering all deaths among women.

Breast cancer is also prevalent in men. This is due to the fact that the breast is composed of identical tissues in respect of both genders. However, it must be remembered that the manifestation of breast cancer in men is some 100 times less common than that in women. Conversely, men with breast cancer are considered to have the same statistical survival rates as women.