This research trial studies the levels of a type of biomarker, circulating tumor cells (CTCs), in the blood of patients with stage I-IV melanoma. A biomarker is a biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. A biomarker may be used to see how well the body responds to a treatment for a disease or condition. Studying samples of blood in the laboratory obtained before and after treatment from patients with melanoma may help doctors learn more about changes that occur in CTC levels and whether they may predict how well patients will respond to therapy.