Nonmelanoma skin cancer usually develops slowly, invading and destroying nearby tissues.
It may take months or years for basal cell or squamous cell carcinomas to
develop. Because of this slow growth, skin cancer can often be detected and
treated early in its development, increasing the chance for a cure.
Basal cell carcinoma
Basal cell carcinoma can affect the surface of the skin where it appears. If it is not treated, it can grow larger and cause problems beneath the skin, sometimes damaging the muscles and bones. Basal cell carcinoma very rarely spreads (metastasizes) to other
parts of the body.
After you have one basal cell carcinoma, you are more likely to have another one develop in a new place. If basal cell carcinoma comes back at the same place (recurs), it may grow
faster and cause more tissue damage.
Squamous cell carcinoma
Squamous cell carcinoma may grow from a small rough spot in sun-damaged skin (actinic keratosis). But this isn't common. Or it may develop from an early form of skin cancer called Bowen's disease. If a squamous cell carcinoma is not treated, it may spread.