Univariate analysis using clinical factors (age, family history, smoking history, initial stage of diagnosis, and endocrine responsiveness) and gene mutation status (TP53, PIK3CA, AKT1, ESR1, and MYC) demonstrated that endocrine responsiveness was the only significant factor affecting overall survival in recurrent breast cancer patients (P = 0.0059). The gene discussed is ESR1; the disease is breast cancer.