Size of o.51 mm means the thickness of the melanoma under the microscope after excision.
The thinner the melanoma, the better the prognosis.
Melanoma of 0.5 size is considered very thin, with very small chance of spreading.
Melanoma level, describes how far a melanoma has penetrated into the skin instead of actually measuring it.
Level 3, means that the cancer involves most of the upper dermis (part of skin).
Measurement of thickness is generally thought to be more useful than the level of penetration in determining a patient's outlook.
But sometimes the level shows that a melanoma is more advanced than doctors may think it is from the measurement of thickness.
The level is used to stage thin melanomas, and thin melanoma that is less than or equal to 1.0 mm thick, without ulceration and level 2 or 3, is staged as T(tumor)1a.
Patients with stage T1a have five-year survival rate of 95%.

Best wishes!
Marija