PTPRC and melanoma: Parsortix-captured CTCs were immunostained for human Mel-A Alexa Fluor 594, human FITC-CD45, and DAPI (markers have been used to define human melanoma CTCs as Mel-A+/DAPI+/CD45− cells; refs. 25, 28) within the Parsortix separation cassette, visualized and counted (Fig. 6A).