ERBB2 and breast cancer: For instance, prior studies have demonstrated that PIK3CA expression is elevated in basal-like, HER2-positive, and triple-negative non-basal (TNnon-B) BC subtypes, while significantly reduced in Luminal subtypes.[41] Given that our data are based on bulk RNA-seq, the overall averaged expression may underestimate PIK3CA’s expression in high-risk subtypes, while the model still captures its upregulation in these subgroups and associates it with poor prognosis.