@rlogan - Welcome to Mayo Clinic Connect. This just has to have been devastating news to hear especially after an X-ray not picking anything up. I am very sorry to hear that your wife has this hard journey ahead of her.

What you can expect in the next few weeks, is that there are a lot of tests! Even if you do not get an immediate appointment with Mayo Clinic be sure to follow up and get the PET-CT done-

Here is what a PET-CT guided scan is about:

Positron emission tomography (PET) uses small amounts of radioactive materials called radiotracers or radiopharmaceuticals, a special camera, and a computer to evaluate organ and tissue functions. By identifying changes at the cellular level, PET may detect the early onset of disease before other imaging tests can. (https://www.radiologyinfo.org/en/info/pet)

The PET radioactive material will light up areas that are hot (inflamed). However, it will not tell what is causing the inflammation. Usually, a biopsy or other test is done to not only show that there is cancer but stage it and name it.

This time is extremely important for you to take one step at a time when things seem to be rushing by you at warp speed.
Concentrate on one appointment at a time. Write down all of your questions and make sure that they are answered. You have the right to know what is going on and to have your questions answered. My first lung cancer was in 1997 and one of the questions that I asked was, "what other questions should I be asking at this point, or what am I missing?"

One other thing that is important: Keep all test results and make sure that you have copies of them. Your wife might want to start a journal to help her express and vent some of her feelings.

Please feel free to ask any questions that you might have.

Why are you surmising that this is likely Extensive Stage Small Cell Lung Cancer?

Merry