Can 6mm lung nodules be cancerous?

I am worried PET scan might show metastases with my mum even though her oxygen saturation level is 98% and her lungs and chest are ok according to her GP. Her nodule was query 6mm (I say query as CT scans are not accurate) on her follow-up CT scan. It was 4mm on the first scan (could still be) Mum says her lips would be a strange colour if metastases were present and her oxygen saturation level would not be as high as it is if that was the case. Don't delete this question like you did with my previous two questions.