stage 4 metastatic melanoma prognosismetastatic melanoma liver prognosismetastatic melanoma in brain prognosismetastatic melanoma in bones prognosismetastatic melanoma survivalmelanoma metastasis to brain prognosismelanoma spread to lungs prognosismelanoma bone metastases prognosismelanoma spread to liver prognosisstage iv metastatic melanoma prognosismetastatic melanoma survival ratemelanoma with brain mets prognosis