My golden retriever has been to the vet atleast 5 times for tumors that I noticed when grooming her. Most of them move as one mass under the skin, but they all came back as fatty tumors and not cancer. I know it is hard to wait for the results, but many times it is not as bad as we think it will be. I have had 2 previous goldens who both dies of cancer, and both were diagnosed after a tumor was biopsied, but they were 8 and 13 years old. 4 sounds a little young to have developed cancer. Unfortunately golden retrievers are very predisposed to lymphoma. One site I researched said 80% of them die from lymphoma. Scary thought. But again, my current golden is 10 1/2 and has been getting lumps since she was 4 or 5. Its a good thing you took her in, but wait for the test results before you panic. Keep up posted!