Together, the lymph vessels and lymph nodes make up the lymphatic system, which circulates a fluid called lymph throughout the body. Lymph contains cells that help fight infection and disease. When breast cancer spreads outside the breast, cancer cells are most often found under the arm in the lymph nodes . In many cases, if the cancer has reached the lymph nodes, cancer cells may have also spread to other parts of the body via the lymphatic system or through the bloodstream. The number of cases per 1,000 women has increased slightly every year over the last 50 years.
Breast cancer occurs in men also, but the number of new cases is small.
Anything that increases a person's chance of developing a disease is called a risk factor. Beginning menstruation at an early age and late age at first birth may also increase the risk of development of breast cancer. History of Breast Cancer - If you have already had breast cancer, you are more likely to develop breast cancer again. Family History - If your mother or sister had breast cancer, you are more likely to develop breast cancer, especially if they had it at an early age. Radiation Therapy - Radiation therapy to the chest that was given more than 10 years ago, especially in women younger than 30 years old, may increase a woman's risk of developing breast cancer.