To diagnose the probability of lip cancer, your doctor will begin by asking about your symptoms and the incidence of cancer in your family. You will then undergo a physical examination where the doctor will examine your affected area, particularly the lips, for swelling and soreness and possible causes of the inflammation. He will also examine the inside of your mouth using a mirror and lights, and feel for any swollen lymph nodes around the neck.
If ample evidence points towards cancer, you will be asked to have a biopsy for confirmation. Additionally, you may also be asked to undertake an exfoliative cytology, wherein a cotton swab will be used to scrape cells from your lips, and then examined under the microscope to detect for any abnormalities.