ICOS and melanoma: In N = 33 melanoma cell lines, a contrasting picture compared to whole tumor tissues from the TCGA cohort emerged: Methylation of CpG sites 1–2, and 6–7 was positively correlated with ICOS mRNA expression, not reaching statistical significance though, whereas methylation status of CpG sites 3–5 showed negative correlation coefficients that were statistically significant for CpG site 4 (ρ = -0.735, P < 0.001) and CpG site 5 (ρ = -0.750, P < 0.001; Fig. 4B).