4 year old with swollen lymph nodes on belly for over 2 months and also cyst in kidney. no viral illness. can it be cancer?

Chances are low: Are the lymph nodes inside- or down in the groin- both are found in virus infections. Did you find out about the cysts with a CT scan? Usually if there is any concern for cancer the doctors will tell you to get further testing One good thing is that if this is going on for 2 months and not causing weight loss or fever then it is less likely cancer- I would recommend talking with your doctor