not sure of diagnosis

My husband was told he had stage 4 lung, liver and spleen cnacer in September. They did 2 pet scans and numerous cat scans. He was treated for mesothelioma which they thought spread to other organs. Today we find out now they think it was stomach cancer all along because of new tumors that were found. These tumors never showed up on anything before. Is this standard procedure this just seems to be a guessing game.

Thanks for listening