@SarahGrove – Early warning system is right! We have a friend who is alive today because he paid attention to the lymph nodes in his neck and jaw.
Luckily he went to his doctor right away when he noticed the swelling and tenderness. He was diagnosed with cancer of the lymph nodes in his jaw.
He was very fortunate to have caught it in time. Especially since, like this article states, the lymph system often carries the cancer cells to other parts of the body.