What Is The Cause And Treatment For Swollen Lymph Nodes?

My son's 5 year old female Rottweiler has many swollen lymph nodes. He is out of town with her and the vet has told him he thinks she has cancer. Took blood and xrays, waiting on results. Is cancer a common problem in young Rottweilers? Is there anything else that would likely cause "all of her lymph nodes to be swollen"? THank you