There are three main types of skin cancer. These are called basal cell carcinomas (also known as rodent ulcers, or BCCs), squamous cell carcinomas (known as SCCs) and malignant melanomas. Malignant melanomas appear as moles or freckles and are quite uncommon. Most skin cancers are either BCCs or SCCs. These appear as red lumps or hardened areas of skin, which grow quite slowly. The area may develop into a sore, could change into an ulcer or become crusted. They do not heal and get better on their own.
As you have an ulcer on your cheek that has not healed then it would be sensible for you to see your GP (family doctor) for a check up. Your GP may either examine you and keep an eye on the ulcer or may take a biopsy of it (removing a small piece of tissue, which may be the whole abnormal area) for examination under a microscope.
The Department of Health has recently given guidelines to GP's about people who come to them with something on their skin that they are worried about. These guidelines say that an appointment should be made with a hospital specialist if the GP suspects you have a BCC or SCC.
If your GP thinks you might have an SCC (or if they have done a biopsy that shows this) then the referral should be urgent, with the specialist seeing you in about two weeks. If they suspect you have a BCC (or if they have done a biopsy that shows that) then the appointment can be less urgent, within about three months. This is because BCCs are very slow growing and virtually never spread so, although they are cancer, treatment is less urgent.
When you see the specialist they will take a full medical history and examine you. Depending on what they see they may do a biopsy in the clinic with a local anaesthetic, or arrange some treatment that may involve cryotherapy (freezing the area around the ulcer) or radiotherapy.
BCCs and SCCs are usually very curable cancers, as are melanomas that are caught at an early stage. As with all cancers, the sooner they are dealt with the better. So if you are worried do go and see your GP for a check up.