Our GSEA analyses showed that the DNMT3B+ tumours with hypermethylation of the promoter region of GATA3 (GATA3–METH group) and the tumours with deleterious somatic alterations of GATA3 (GATA–LOFDEL group) shared the same molecular signatures related to breast cancer aggressiveness: proliferation, cell cycle, DNA replication, metastasis, aberrant activation of tissue-specific genes, and enrichment in breast cancer precursors. The gene discussed is GATA3; the disease is breast cancer.