The breast has a network of blood vessels (called the vascular system) and lymph channels (lymphatic system) that carry blood and fluid back and forth from your breast tissue to the rest of the body. They are the "highways" that bring in nourishment and remove used blood and the waste products of cell life.
Vascular or lymphatic system invasion happens when breast cancer cells break into the blood vessels or lymph channels. This increases the risk of the cancer traveling outside the breast or coming back in the future. Doctors can recommend treatments to help reduce this risk.
Your pathology report will say “present” if there is evidence of vascular or lymphatic system invasion. If there is no invasion, your report will say “absent.” Lymphatic invasion is different from lymph node involvement. The lymph channels and lymph nodes are part of the same system, but they are looked at and reported separately.