GAPDH and melanoma: To account for the contribution from cellular variations in the skin, for example, distribution of dermal cells and immunological infiltrates surrounding the tumor, to the variation in ACTB and GAPDH gene expression, we conducted RNA quality assessment by GAPDH multiplex RT-PCR and reference gene expression stability analyses by qRT-PCR using sections of non-cancerous cutaneous samples removed from five of the melanoma patients (1, 4, 7, 8 and 13).