Could i have mets in i brain, liver and skin with stage 3 metastatic melanoma?

Stage 4: When melanoma has spread to the brain or liver, it is stage 4. Left alone long enough, stage 3 will become stage 4.

No easy answer: You won't know unless they are causing symptoms or are large enough to be seen on a scan. So it will not be called stage 4 unless this happens. They may be present as microscopic mets with no symptoms.

Melanoma: By definition, stage 3 melanoma patients have disease that is limited to the primary site and regional lymph nodes. A metastatic workup needs to be performed on all stage 3 patients to make sure that they do have mets to brain, liver and other organs making them a stage 4 patient.