Metastatic Breast Cancer refers to the advanced stage of breast cancer. Whereby the cancer spreads out to distant organs. Breast cancer has the unique potential to spread to any part of the body. It first spreads to the bone and then lungs and liver. Knee is a far flung body part and since your don't have it anywhere above the knee so the problem in the knee might be something else. For details see the link below:
www.imaginis.com
www.imaginis.com