Breast cancer is usually positive for CK7 expression and negative for CK20 expression, in addition, positive CK7 expression and negative CK20 expression are also present in ovarian, lung, and thyroid cancers, and CK20 is usually expressed in colorectal and other gastrointestinal cancers, and rarely positive in breast cancer [18–20]. The gene discussed is KRT20; the disease is thyroid cancer.