• Is the second leading cause of cancer deaths in women.
• Annually afflicts over 180,000 Americans.
• Takes the lives of more than 46,000 people in the United States every year.

PROGRESS IN MEDICAL RESEARCH

What is the importance of animals to breast cancer research?

Animals have played, and continue to play, important roles in breast cancer research. Rats and mice are especially useful because certain strains can develop cancer spontaneously, as well as by viral and chemical induction. With their short lifespan the results of testing can be achieved much more quickly.

Using cancer-causing chemicals to induce breast cancer in rats has been a powerful model for understanding the role of estrogen and other hormones in breast cancer development. The protective role of early pregnancy, which we realized from studies among women, is mimicked in rats and the mechanism of this protection, clarified by rat experimentation, may eventually provide ways to prevent breast cancer in women. Rat breast cancer models have also proven useful in understanding the role of dietary factors in breast cancer causation.

Mouse mammary cancer models, also a mainstay of breast cancer research, have been particularly instructive in understanding the genetic and endocrine bases of breast cancer development; in identifying genes which cause, or prevent, cancer; and developing an understanding of the factors that may influence the progression of precancerous lesions to tumors, and on to malignant, metastatic cancers. Mouse cancer models are also used in preclinical testing of new drugs and combinations of drugs.

What's ahead for breast cancer research?

Within the past ten years or so, animal research in breast cancer has expanded to include the growth of human breast cancers and, even more recently, human precancerous breast lesions, in mice with no immune systems. These xenograft models mirror the pathological, biological, and clinical pictures of human breast cancer and allow for experimentation which is not possible in women. Such models are being used to test new methods of treatment and prevention, as well as to identify genetic and environmental factors that influence breast cancer development and growth. Research continues to lead to improved treatments and longer disease free survival.