Can leukoplakia be a cancer?

Can be. Leukoplakia may be a precursor to cancer and needs to be evaluated by a doctor. Sometimes a biopsy and examination of the tissue by a pathologist is required.
Can be pre-cancerous. Leukoplakia is a thickening of the lining of the mouth tissues and is due to reaction from local irritation or inflammation and is common in tobacco users. It can be a pre-cancerous condition and over time can become cancerous in a significant number of cases (up to 15-20%). Checking with your doctor to see if a biopsy may be necessary is the next step.