PTGS2 and breast neoplasm: These features were also characteristic of human claudin-low tumors in the METABRIC cohort [6, 7], which showed significantly higher expression levels of both PTGS2 and CD274 compared to non-claudin-low breast tumors (p < 0.001 for both, two-tailed Wilcoxon rank-sum test) and compared specifically to basal-like tumors (p = 0.004 and p < 0.001, respectively) (Fig. 5c).