ESR1 and breast cancer: Infectious agents such as Epstein-Barr virus and Toxoplasma gondii infection have also been examined, with results showing that Epstein-Barr virus infection being associated with a higher BC risk among ER + , PR + , and HER2 + patients [18], while Toxoplasma gondii infection being associated with a lower BC mortality and progression risk [HR (95% CI):0.60 (0.37–0.99) for mortality; HR (95% CI):0.67 (0.46–0.98) for progression] [38].