The lymph system is a series of vessels in your body similar to your blood vessels. The job of the lymph system is to absorb fluid that has escaped from the blood vessels (into the interstitial space) so that the fluid can be returned to the cardiovascular system (via the subclavian veins). As the fluid is making its way through the lymph vessels it also gets filtered through lymph nodes. These nodes contain white blood cells that can eat foreign particles or cellular debris as well as stimulate an immune response. Because the lymph nodes may swell when battling an infection, a doctor may palpate them to help in his/her diagnosis.
Watch this CancerQuest video to learn more about the lymph system and to understand a lymph node biopsy.
Lymphatic system with cancer spread animation and lymph node animation
Understanding the lymphatic system
Compare the cardiovascular and lymph systems
A number of videos at CancerQuest
Cancer Staging - read this page to get an overview of how they 'stage' the severity of cancer.