PIK3CA and breast cancer: A previous study showed that PD-1 expression in TILs was associated with a higher rate of mutations, whereas PD-L1 expression in tumours showed the opposite association.33 Breast cancers with mutated TP53 exhibit higher PD-1 in TILs compared with breast cancers that harbour other mutations (eg, PIK3CA) or those without mutations.33 In contrast, PD-L1 expression in tumour cells does not correlate with mutation status.33