If chest xray comes back abnormal and a ct scan is needed - does that mean cancer? if not cancer what are other possible answers

Cannot tell: An abnormal chest xray is often followed by more testing, such as a ct, to try to tell why it is abnormal.

Not usually: Most of the abnormalities seen on a chest xray are not cancer. Old (or new) infections, scarring or fibrosis, benign sclerosis in a rib and benign tumors of the lung or lung lining are all possible, as well as lung cancer. A chest xray can sometimes predict if lung cancer is more likely, but a ct will provide a more definite assessment of the likelihood of cancer. A biopsy is sometimes needed.