Does abnormal or reactive lymph nodes mean cancer? how common would a lymphatic cancer be in an 18 year old?

Lymphadenitis: Or swollen lymph nodes due to viral or bacterial infection. The swollen lymph nodes caused by cancer is not very common condition. I don't think that your case is any different. . If concerned, check with your pcp.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.