PLK2 and melanoma: With regard to the genes specifically up-regulated in the MCSP CTC fraction, the majority have been involved in metastasis (LOXL4, ST6GALNAC2, PYGL), tumour growth (PLK2, CYSTM1, GLUL), and/or melanoma biology (SEC31A, WIPI1, SKP1) [42,43,45,46,47,48,49,50,51,52,53].