There are two basic cell types of melanoma as seen with the microscope. These are spindle and epithelioid. Most melanomas have a combination of these 2 cell types. Only if the eye is removed or the tumor resected can the doctor judge the cell type. Melanomas with predominantly spindle cells have thin elongated cells and imply better prognosis. Epithelioid cell type melanoma has round cells and imply worse prognosis.
There are two basic types of melanoma by genetics: high risk and low risk. The doctor can sample the tumor before treatment to tell the patient if the tumor carries a high or low risk for metastasis.