The breast also contains arteries, veins, nerves, lymph nodes, and lymph vessels. Breast cancer can spread through the lymph vessels and veins to other parts of the body. The main vein is the mammary vein. Most of the smaller veins drain into this vein. Some veins drain into areas under the armpit, or along the ribs. The blood stream can help spread cancer cells from the breast to other organs in the body.