ISG15 and breast cancer: Moreover, when we distributed the mRNA expression of ISG15 according to histological tumour subtypes, high mRNA expression of ISG15 was significantly associated with ductal no special type (NST) BC compared to lobular BC subtype in the METABRIC cohort (p < 0.001), but not in the TCGA cohort (p = 0.710) (Table 1).