My chest CT stated that " Beneath the imaged abdomen, no significant abnormalities seen." What does it mean? Can it rule out stomach cancer?

Negative. Based only on the sentence you cited, it sounds like they did not see anything abnormal. Disclaimers: 1. No scan is perfect. 2. We are not seeing the whole report. 3. We do not know why your doc ordered it (is it because of your lymph nodes?). Your doc has to interpret this in context, talk to him/her. If you have GI symptoms, you may need an endoscopy. That is the best way to diagnose gastric CA.