pet scans

A patient is being treated by an oncologist and is diagnosed with colon cancer and then is referred to a pulmonologist for lung nodule who then orders a pet scan; Which diagnosis code is primary for the pet scan?

re: pet scans

The primary diagnosis is the lung nodule and second is colon cancer. The pulmonologist needs to find out if the nodule is malignant or not. If malignant, needs to evaluate it for primary lung cancer or lung metastasis related to the colon cancer.