Stage IV lung cancer is never a good sign. It means that it’s spread outside the original organ. For Lung cancer that frequently means the brain.
Cancer sucks. A lot.
I had a friend - who had never smoked, btw - who only discovered she had lung cancer when her back began to hurt because the cancer had spread and a tumor was growing into her spine. She had surgery and chemo/radiation but she died 6 months later.
Cancer does indeed suck.