Increased expression of ESR1 and consequently of the ESR1/ESR2 ratio has been shown to be associated to aggressive prognostic and worse overall survival in patients with papillary thyroid carcinoma (42), whereas decreased ESR1/ESR2 ratio in endometriosis-like phenotype mice lead to low response to P4 and subfertility (43). The gene discussed is ESR2; the disease is thyroid gland papillary carcinoma.