My Dad Had A Chest X-ray Because Of His Smoking

My dad had a chest X-ray because of his smoking history and asbestosis and copd. He has one every year. He also has a cat scan every two years. This time they said he had enlarged lymph nodes in his chest. They took another cat scan and said he had swollen lymph Nodes in his abdomen too. He just had a pet scan and he is getting ready for a biopsy. The dr. said the pet scan would not show if there was anything else anywhere else, which confused me, because I thought that was the whole point of a pet scan. The dr. said they were just looking at his lymph nodes. His biopsy is the 20th. I suppose my questions are, is this common procedure to do a pet scan that tells you nothing? And what are the odds it could be something else other than cancer? I just feel anxious. Am I overreacting when there is nothing to know yet? I mean, if not cancer, what else could it be? And if it is cancer, aren't the lymph nodes the last place they go to in late stages? Please help me understand. I am a nervous wreck. Thanks very much, Melissa