The patterns of mutations in TP53 with PIK3CA allowed us to identify four molecular clusters in both PR− and PR+ Luminal breast cancers, namely PIK3CA/TP53-mutant (Cluster 1), PIK3CA-mutant/TP53 wild-type (Cluster 2), PIK3CA wild-type/TP53-mutant (Cluster 3), and PIK3CA/TP53 wild-type (Cluster 4). The gene discussed is PIK3CA; the disease is breast cancer.