stage iv metastatic melanoma prognosisclark level iistage iv melanoma survivalstage iv melanoma survival ratemelanoma clark level 2stage 4 melanoma prognosisstage 4 metastatic melanoma prognosisprognosis for stage 4 melanoma cancerstage 4 melanoma survivalclark 4 melanoma prognosisstage iv breast cancer treatmentstage iv lung cancer