Immunohistochemistry was used on patient tumor samples to assess the relative expression of proteins that are known to be positively (Ki67; estrogen receptor-α (ERα)) and negatively (progesterone receptor (PGR); Krüppel-like factor 9 (KLF9); phosphatase and tensin homolog (PTEN)) associated with EC. Here, ESR1 is linked to neoplasm.