Get a new vet. If he found a "shadow", meaning some kind of mass, he should have had a biopsy done, as well as a blood panel to determine which numbers were off, if any.
Those combined will allow the vet to make an "it could be this, or could be that", somewhat of a diagnosis.
I'm only saying this because I just went through it. I found, well was referred to the best vet in the whole world! I am thankful everyday I found him.
The 1st vet I took her to didn't even bother to misdiagnose her, let alone diagnose her.
He wanted to do about $3000 worth of "vitamin testing". What an a-hole.
He pulled the mass out and it was a big clump of fur. I’m checking out the vet closer to the house we just bought.
I just got some bad news. My wife informed me that the cat is cutting into my gun money.