The present invention relates to methods for diagnosing, staging and treating cancer, in particular melanoma. In particular, the present invention provides methods for determining the stage/type of a cancerous disease, comprising detecting somatic alterations of the DNA of one or more disseminated cancer cells (DCCs), obtained after homing to a distant organ, such as lymph node; and determining the somatic evolution of the DCC(s) based on the detected somatic alterations, wherein the somatic evolution is indicative of the stage/type of the cancerous disease.