ESR1 and breast cancer: ER and PR positivity is suggestive of metastatic disease from breast cancer, but both ER and PR can be positive in 32% and 12% of patients with cancer of a gastric origin, respectively, which indicates these receptors cannot represent suitable biomarkers to discriminate between breast cancer metastasis to the stomach and primary gastric cancer.[45] In our literature review, the positive rates of ER and PR in the metastatic location were as high as 86.67% and 46.67%, respectively.