As compared with the TCGA cohort, younger breast cancer patients (≤35 years) in our cohort had higher mutation rates in TP53 (51% vs. 30%) and ERBB2 (34% vs. 24%), and lower mutation rates in PIK3CA (25% vs. 30%) and GATA3 (15% vs. 24%). The gene discussed is PIK3CA; the disease is breast carcinoma.