The objective of the present study was to assess the usefulness of serum concentrations of methylated Estrogen Receptor1 (ESR1) and Stratifin (14-3-3-σ) gene promoters in breast cancer patients in two very different clinical situations: i) treated and with no evidence of residual or recurrent disease, and ii) treated and with detected metastatic breast cancer. The gene discussed is ESR1; the disease is breast carcinoma.