This evidence, bearing the polyclonal heterogeneity toward ER + breast cancer evolution, attests to the potential benefit of liquid biopsy CGP to capture different disease progression patterns expressing both polyclonal ESR1 and MAPK mutations significantly affecting survival outcomes or to distinguish between clonally dominant or sub-clonal variants [240] helping in the interpretation of tumor heterogeneity through the creation of genomic signatures related to the different histological profiles of breast cancer. The gene discussed is ESR1; the disease is neoplasm.