How And Why Cancer Spreads: Breast Cancer

Content provided by the Faculty of the Harvard Medical School

How and why cancer spreads

Most people visualize a malignant tumor as steadily growing, and they may assume that if a lump is small, it's an early cancer. This may not be true. Tumor size alone doesn't indicate a cancer's severity.

Although most of the time smaller tumors are less likely to have spread, the aggressiveness of a particular cancer is a major factor in how much it spreads. Some small tumors may quickly travel to the lymph nodes, and some large ones may not spread at all.

Another factor is the patient's immune system. By the time a tumor is found, cancer cells may have been present for some years, but the immune system has controlled their proliferation. Experts believe that at some point, in some women, the malignant cells become too numerous for the body's immune system to handle; the cancer then begins to metastasize, or spread.

Cancer treatment today is based on the premise that reducing the number of cancer cells - by removing the tumor and killing cancer cells that have spread to other organs - can turn the tide in favor of the body and its natural defenses.

The risk for most forms of cancer rises with age, and breast cancer is no exception. At age 20, your risk is very low, but by age 50, one in every 36 women will be diagnosed with breast cancer within the next 10 years. The risk continues to rise throughout life.

Last updated:	April 23, 2007